The surface and atmospheric chemistry of solar system bodies---including the Earth---are heavily influenced by transient particle events from the Sun like coronal mass ejections (CMEs) and solar energetic particles (SEP). These events, alongside the electromagnetic (EM) radiation of solar flares, comprise what we call space weather. The energy of both the EM and particle events are expected to have been orders of magnitude higher when the Sun was much younger, which raises questions with regards to the evolution of angular momentum, chemistry, and habitability throughout our solar system's history. Studying this history requires we study young stars as proxies for the young Sun, but the particle environment of other stars is notoriously difficult to study and CMEs or SEPs are even more so due to their transience and the multi-wavelength nature of their signatures. Fully characterizing an event thus requires extensive, coordinated monitoring across many instruments.
\r\n\r\nTo address this requirement for studying space weather, I present the beginning of the Space Weather Around Young Suns (SWAYS) program in this thesis. This program includes the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) for identifying stellar analogs of solar type II and III bursts which are associated with bulk plasma motion from the Sun. The SWAYS program also includes Flarescope which I designed and built to detect photometric signatures of flares from solar-type stars with high precision at optical wavelengths. With Flarescope and the OVRO-LWA, I have collected more than 800 hours of simultaneous data on six young, solar-type stars and have developed a framework for analyzing the results of their coordination. This thesis includes a technical overview of Flarescope\u2019s design, a summary of its performance with the OVRO-LWA, and the framework for using the two instruments to search for signatures of transient particle flux. I supplement the significance of simultaneous observations of solar-type stars at optical and radio wavelengths with my work with the Very Large Array Sky Survey and Transiting Exoplanet Survey Satellite data. In this work, I identify unprecedented stellar radio emission and develop the relationship between such emission and stellar superflares. In all, this thesis illustrates the significance of simultaneous radio and optical observations for constraining stellar space weather and highlights the feasibility of multi-wavelength monitoring.
" }, { "name": "Huang, Yuping", "degree": "PhD", "year": "2025", "title": "Building a Radio Camera in Search of Exoplanet Magnetospheres", "advisor": "Hallinan, Gregg W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072025-035609195", "creators": [ { "name": { "family": "Huang", "given": "Yuping" }, "id": "Huang-Yuping", "orcid": "0000-0003-4267-6108", "display_name": "Huang, Yuping" } ], "advisors": [ { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "advisor", "display_name": "Hallinan, Gregg W." } ], "committee": [ { "name": { "family": "Howard", "given": "Andrew W." }, "id": "Howard-A-W", "orcid": "0000-0001-8638-0320", "role": "chair", "display_name": "Howard, Andrew W." }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "member", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "Ravi", "given": "Vikram" }, "id": "Ravi-Vikram", "orcid": "0000-0002-7252-5485", "role": "member", "display_name": "Ravi, Vikram" }, { "name": { "family": "Knutson", "given": "Heather A." }, "id": "Knutson-H-A", "orcid": "0000-0002-5375-4725", "role": "member", "display_name": "Knutson, Heather A." }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Stevenson", "given": "David John" }, "id": "Stevenson-D-J", "orcid": "0000-0001-9432-7159", "role": "member", "display_name": "Stevenson, David John" } ], "option_major": [ "astrophys" ], "doi": "10.7907/5wym-kg12", "abstract": "Detections of exoplanetary magnetic field will add an important axis for understanding their properties. It is also important to place planets in the context of their stars, many of which exhibit different activity paradigms from that of the Sun. In this thesis, I attempt to characterize the energetic particle environment around young M dwarf using existing millimeter observations, and attempt to detect an exoplanetary magnetic field.
\r\n\r\nThe detection of exoplanetary magnetic field requires both exquisite sensitivity and long-term monitoring at low (<100MHz) radio frequencies. I dedicated a significant efforts to the expansion of the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), especially the complete redesign of the compute cluster. I set up the compute infrastructure and wrote the processing pipeline that made a search through 3 petabytes of data for the radio emission from Tau Bootis b, covering multiple orbits of the planet, possible.
\r\n\r\nThe OVRO-LWA will ultimately transition to a radio camera paradigm, where the telescope operates continuously and produces images as its data product. The 2000-element Deep Synoptic Array (DSA-2000) will be the first true radio camera optimized for surveys. I validated key design requirements of the DSA-2000 through forward modeling, and prototyped the radio camera on the OVRO-LWA.
" }, { "name": "Chen, Ge", "degree": "PhD", "year": "2024", "title": "Localized Fast Radio Bursts Using DSA-110", "advisor": "Ravi, Vikram", "url": "https://resolver.caltech.edu/CaltechTHESIS:12192023-224904219", "creators": [ { "name": { "family": "Chen", "given": "Ge" }, "id": "Chen-Ge", "orcid": "0000-0003-2867-4544", "display_name": "Chen, Ge" } ], "advisors": [ { "name": { "family": "Ravi", "given": "Vikram" }, "id": "Ravi-Vikram", "orcid": "0000-0002-7252-5485", "role": "advisor", "display_name": "Ravi, Vikram" } ], "committee": [ { "name": { "family": "Kasliwal", "given": "Mansi M." }, "id": "Kasliwal-Mansi-M", "orcid": "0000-0002-5619-4938", "role": "chair", "display_name": "Kasliwal, Mansi M." }, { "name": { "family": "Ravi", "given": "Vikram" }, "id": "Ravi-Vikram", "orcid": "0000-0002-7252-5485", "role": "member", "display_name": "Ravi, Vikram" }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "orcid": "0000-0002-9656-4032", "role": "member", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "member", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "Weinstein", "given": "Alan Jay" }, "id": "Weinstein-Alan-J-Physics", "orcid": "0000-0002-0928-6784", "role": "member", "display_name": "Weinstein, Alan Jay" } ], "option_major": [ "physics" ], "doi": "10.7907/xchy-q017", "abstract": "Fast Radio Bursts (FRBs) are \u00b5s- to ms- scale, energetic (1040~46 erg s-1) bursts detected in the radio frequency (110 MHz to 8 GHz). They primarily originate from extragalactic sources and are likely to originate from compact object sources. \r\n The exact nature of the sources and the emission mechanisms remain inconclusive.
\r\n \r\nThe first FRB was not confirmed until 2007. By early 2023, over 600 FRBs have been reported, and about 40 FRBs have been associated with an individual host galaxy. The rapid growth in sample size has helped to greatly narrow down the number of source models. Neutron stars, especially magnetars, have been the most popular source candidate, although other possibilities still remain.
\r\n\r\nIn this thesis, we explore a few observational methods to study the potential FRB source and host environments. In Chapter 2, we demonstrated a method to constrain the energy ratio emitted from the FRB's multiwavelength transient counterparts as compared to the FRB energy themselves. We used the existing multiwavelength transient blind survey database and the current FRB population fluence distribution to produce tighter constraints than most targeted surveys. In Chapter 3, we investigated whether or not the persistent radio source associated with FRB 121102 could be an AGN using the VLA monitoring data and a new Keck optical spectrum. We constrained the emission source radius to be 1017~18 cm based on the low level of variability in the VLA radio flux measurements presented in this work as compared to the Galactic scintillation theory and other published results by VLBI. We estimated the mass of the potential black hole to be \u227e104~5 M\u2609 based on the H\u03b1 line width in the Keck spectrum. We concluded that the source is unlikely an AGN based on the size, mass, and radio luminosity, and that the persistent radio source could be explained by an isolated neutron star with a pulsar wind nebula. In Chapter 4, we showed the burst morphology of a sample of 21 FRBs detected by DSA-110 during part of the commissioning period in 2022, including 16 localized FRBs with optical spectra. We explored the potential correlation between burst morphology and host properties. We found a strong correlation between the host H\u03b1 luminosity and FRB burst energy that is likely a result of observational selection effects. We measured the scintillation timescales and found most of them close to the predicted Galactic scintillation timescales. In Chapter 5, we summarize the thesis and very briefly discussed potential extensions of the above methods for the study of FRB sources.
" }, { "name": "Yadlapalli Yurk, Nitika", "degree": "PhD", "year": "2024", "title": "Interferometric Millimeter Observations of the High Energy Universe", "advisor": "Ravi, Vikram; Bouman, Katherine L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08172023-032920075", "creators": [ { "name": { "family": "Yadlapalli Yurk", "given": "Nitika" }, "id": "Yadlapalli-Yurk-Nitika", "orcid": "0000-0003-3255-4617", "display_name": "Yadlapalli Yurk, Nitika" } ], "advisors": [ { "name": { "family": "Ravi", "given": "Vikram" }, "id": "Ravi-Vikram", "orcid": "0000-0002-7252-5485", "role": "advisor", "display_name": "Ravi, Vikram" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "co-advisor", "display_name": "Bouman, Katherine L." } ], "committee": [ { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "orcid": "0000-0002-3330-5439", "role": "chair", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "member", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "orcid": "0000-0002-9656-4032", "role": "member", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Ravi", "given": "Vikram" }, "id": "Ravi-Vikram", "orcid": "0000-0002-7252-5485", "role": "member", "display_name": "Ravi, Vikram" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." } ], "option_major": [ "astrophys" ], "doi": "10.7907/g8fs-5q44", "abstract": "This thesis explores what can be accomplished in the ways of time-domain astrophysics with a variety of scales of millimeter interferometry. I touch upon techniques in instrumentation, theory, observation, and computation, showcasing the breadth and richness of the field.
\r\n\r\nThe transient millimeter sky is largely comprised of synchrotron sources whose physical properties are just beginning to be revealed. We are entering an age where new wide-field surveys will exponentially increase the number of known transients, including the first wide-field millimeter survey capable of significant transient detections. As we approach this era, resources dedicated to monitoring and follow-up become increasingly more important.
\r\n\r\nA significant part of my work involves design and commissioning for a new single baseline millimeter interferometer at the Owens Valley Radio Observatory called SPRITE. Uniquely positioned as a dedicated transient follow-up telescope, SPRITE has the ability to observe nearby transients with a relatively high cadence. In this thesis, I also highlight two specific classes of sources for which millimeter observations may be particularly interesting. I present predictions for millimeter emission from supernovae interacting with dense circumstellar media and discuss their rates of detection in upcoming surveys. I additionally present lower frequency spatially-resolved radio observations of an X-ray binary in an active state.
\r\n\r\nOn the other extreme, this thesis also explores the use of very long baseline interferometry to investigate how high resolution images of supermassive black holes vary over the timescale of a year. In 2017, the Event Horizon Telescope Collaboration (EHTC) observed the supermassive black hole in nearby galaxy M87, producing the first resolved image of the shadow of a black hole and potentially revealing intra-day variability of the observed synchrotron emission around the shadow. I present work on the imaging and preliminary analysis of the 2018 epoch of EHT observations of the black hole in M87, and discuss the EHTC\u2019s conclusions of intra-day and year-long variations in the images.
" }, { "name": "Bochenek, Christopher David", "degree": "PhD", "year": "2021", "title": "The Progenitors of Fast Radio Bursts", "advisor": "Ravi, Vikram; Kulkarni, Shrinivas R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05192021-014425301", "creators": [ { "name": { "family": "Bochenek", "given": "Christopher David" }, "id": "Bochenek-Christopher-David", "orcid": "0000-0003-3875-9568", "display_name": "Bochenek, Christopher David" } ], "advisors": [ { "name": { "family": "Ravi", "given": "Vikram" }, "id": "Ravi-Vikram", "orcid": "0000-0002-7252-5485", "role": "co-advisor", "display_name": "Ravi, Vikram" }, { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "orcid": "0000-0001-5390-8563", "role": "co-advisor", "display_name": "Kulkarni, Shrinivas R." } ], "committee": [ { "name": { "family": "Hillenbrand", "given": "Lynne A." }, "id": "Hillenbrand-L-A", "role": "chair", "display_name": "Hillenbrand, Lynne A." }, { "name": { "family": "Ravi", "given": "Vikram" }, "id": "Ravi-Vikram", "orcid": "0000-0002-7252-5485", "role": "member", "display_name": "Ravi, Vikram" }, { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "orcid": "0000-0001-5390-8563", "role": "member", "display_name": "Kulkarni, Shrinivas R." }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "orcid": "0000-0002-9656-4032", "role": "member", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Steidel", "given": "Charles C." }, "id": "Steidel-C-C", "orcid": "0000-0002-4834-7260", "role": "member", "display_name": "Steidel, Charles C." } ], "option_major": [ "astrophys" ], "doi": "10.7907/7tsx-x524", "abstract": "Fast radio bursts (FRBs) are millisecond duration pulses of radio emission that are bright enough to be seen from other galaxies. The nature of the objects that produce fast radio bursts has captivated the interest of astronomers since their discovery in 2007. The durations and energetics of FRBs imply a compact, highly magnetized progenitor, making magnetars a popular progenitor candidate. However, it is difficult to pin down the progenitors of FRBs because they occur so far away. In this thesis, I will present the Survey for Transient Astronomical Radio Emission 2 (STARE2), an experiment designed to detect FRBs in the Milky Way. I will present a formalism through which to interpret the results of this experiment and demonstrate our experiment's effectiveness with the detection of a solar burst. Using STARE2, we discovered the first FRB that originated within the Milky Way, FRB 200428. This FRB was traced back to the Galactic magnetar SGR J1935+2154. The energetics, spectro-temporal properties, host galaxy, environment, and X-ray counterpart are all consistent with the properties of extragalactic FRBs. In addition, the high volumetric rate of these bright radio bursts from magnetars is consistent with the volumetric rate of FRBs, implying that magnetars are the dominant channel of FRB production. I will then develop a novel statistical technique to compare transient host galaxies in order to evaluate whether the hosts of extragalactic FRBs are consistent with a magnetar origin. I will find that the hosts of FRBs are consistent with the hosts of core-collapse supernovae, supporting the hypothesis that magnetars produce FRBs. Finally, I will present two ideas for future observing campaigns to find FRBs from M82 and more extremely bright pulses from Galactic magnetars.
" }, { "name": "Anderson, Marin Mallory", "degree": "PhD", "year": "2019", "title": "Adventures Through Time and Phase Space: Characterizing the Dynamic Radio Sky, From MHz to GHz, From Seconds to Years", "advisor": "Hallinan, Gregg W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222019-125805458", "creators": [ { "name": { "family": "Anderson", "given": "Marin Mallory" }, "id": "Anderson-Marin-Mallory", "orcid": "0000-0003-2238-2698", "display_name": "Anderson, Marin Mallory" } ], "advisors": [ { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "advisor", "display_name": "Hallinan, Gregg W." } ], "committee": [ { "name": { "family": "Kasliwal", "given": "Mansi M." }, "id": "Kasliwal-Mansi-M", "orcid": "0000-0002-5619-4938", "role": "chair", "display_name": "Kasliwal, Mansi M." }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "member", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "orcid": "0000-0002-9656-4032", "role": "member", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "orcid": "0000-0001-5390-8563", "role": "member", "display_name": "Kulkarni, Shrinivas R." }, { "name": { "family": "Mawet", "given": "Dimitri" }, "id": "Mawet-D", "orcid": "0000-0002-8895-4735", "role": "member", "display_name": "Mawet, Dimitri" } ], "option_major": [ "astrophys" ], "doi": "10.7907/D28A-YQ77", "abstract": "Time domain radio astronomy is on the cusp of a revolution. This is particularly true at low radio frequencies, where wide-field arrays are conducting deeper surveys than ever before, in pursuit of elusive transient phenomena. This thesis has opened an unprecedented window on the dynamic radio sky, spanning a wide range in frequency -- from MHz to GHz -- and a wide range of phenomena -- from searches for coherent radio bursts indicative of coronal mass ejections from nearby stars, to the detection of incoherent synchrotron emission from an outflow associated with the tidal disruption of a star by a supermassive black hole at the center of a galaxy.
\r\n\r\nA significant part of this work has involved the building of the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), a uniquely powerful radio telescope, with the ability to image the entire viewable sky at a 10 second cadence and across nearly 60 MHz of bandwidth. With the OVRO-LWA, I have developed the methods and techniques necessary for pushing further into unexplored regions of radio transient phase space, in the pursuit of sources of radio emission that provide unique insight into various astrophysical phenomena. This includes the follow-up of gravitational wave events in order to search for the signatures of prompt, coherent radio emission associated with compact object mergers, as well as targeted searches for stellar and exoplanetary radio emission as a means of better understanding planetary habitability.
" }, { "name": "Eastwood, Michael William", "degree": "PhD", "year": "2019", "title": "Searching for the Cosmic Dawn with the Hyperfine Structure Transition of Hydrogen", "advisor": "Hallinan, Gregg W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05272019-174203596", "creators": [ { "name": { "family": "Eastwood", "given": "Michael William" }, "id": "Eastwood-Michael-William", "orcid": "0000-0002-4731-6083", "display_name": "Eastwood, Michael William" } ], "advisors": [ { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "advisor", "display_name": "Hallinan, Gregg W." } ], "committee": [ { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "orcid": "0000-0002-9656-4032", "role": "chair", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "member", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "Hirata", "given": "Christopher M." }, "id": "Hirata-C-M", "orcid": "0000-0002-2951-4932", "role": "member", "display_name": "Hirata, Christopher M." }, { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "orcid": "0000-0001-5390-8563", "role": "member", "display_name": "Kulkarni, Shrinivas R." }, { "name": { "family": "Pearson", "given": "Timothy J." }, "id": "Pearson-T-J", "orcid": "0000-0001-5213-6231", "role": "member", "display_name": "Pearson, Timothy J." }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." } ], "option_major": [ "astrophys" ], "doi": "10.7907/DYPP-JP25", "abstract": "The 21 cm hyperfine structure transition of neutral hydrogen promises to open a window into the first billion years of the Universe (z > 6). With the exception of rare lines of sight towards exceptionally distant and luminous galaxies, this period of the universe's history remains largely unexplored. During this time the 21 cm transition is expected to be detectable as a 10--100 mK perturbation in the thermal Cosmic Microwave Background (CMB) spectrum.
\r\n\r\nDue to the large field of view of low frequency radio telescopes (typically composed of dipole antennas) and the fact that the line of sight distance can be inferred from the measured frequency of the transition, the ultimate goal of 21 cm cosmology is to produce three dimensional tomographic maps of the 21 cm brightness temperature. In this way, the formation of the first stars and galaxies will be revealed through their influence on the neutral gas around them.
\r\n\r\nThis thesis saw the construction of the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), a new low frequency (27--85 MHz) radio telescope located near Bishop, California. Composed of 288 crossed-dipole antennas, the OVRO-LWA is capable of imaging the entire visible hemisphere in a single 13 s snapshot image with 8 arcmin angular resolution.
\r\n\r\nThe primary challenges faced by efforts to detect the highly redshifted 21 cm transition are seeing past the blinding glow of foreground radio emission that is five orders of magnitude brighter than the cosmological emission, and calibrating the instrument to a level where it's possible to make the separation between foreground emission and the 21 cm signal. In this thesis I will present foundational work using the OVRO-LWA to place upper limits on spatial fluctuations of the 21 cm transition during the Cosmic Dawn---the period of first star formation.
\r\n\r\nIn this thesis I present the highest angular resolution maps of the full sky below 100 MHz, and generated with a new widefield imaging technique that is specialized for drift scanning interferometers. These sky maps are a 10-fold improvement in angular resolution over existing maps at comparable frequencies, and are publicly available now for use in modeling and subtracting the contamination of foreground emission in 21 cm experiments.
\r\n\r\nUsing a 28 hr integration with the OVRO-LWA, I place to-date the most constraining upper limits on the amplitude of the 21 cm spatial power spectrum at the Cosmic Dawn, and the first limits at z > 18. Although the current constraints \u0394212 \u2272 (104mK)2 do not meaningfully restrict the parameter space of models of early star formation, they do inform the design and calibrations necessary for future measurements to push towards a detection of the high-redshift 21 cm transition. In making this measurement I demonstrate the application of a new foreground filter that accounts for the full covariance of the foreground emission, and provide an updated measurement of the foreground angular covariance. Finally, I interpret the limiting factors in this measurement and determine the instrumental calibration and characterization requirements the OVRO-LWA will need to achieve in order to make a detection of the 21 cm power spectrum of the Cosmic Dawn.
" }, { "name": "Monroe, Ryan McKay", "degree": "PhD", "year": "2018", "title": "Gigahertz Bandwidth and Nanosecond Timescales: New Frontiers in Radio Astronomy Through Peak Performance Signal Processing", "advisor": "Hallinan, Gregg W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042018-004220017", "creators": [ { "name": { "family": "Monroe", "given": "Ryan McKay" }, "id": "Monroe-Ryan-McKay", "orcid": "0000-0002-0026-4546", "display_name": "Monroe, Ryan McKay" } ], "advisors": [ { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "role": "advisor", "display_name": "Hallinan, Gregg W." } ], "committee": [ { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "role": "chair", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "D'Addario", "given": "Larry R." }, "id": "D'Addario-L-R", "role": "member", "display_name": "D'Addario, Larry R." }, { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "member", "display_name": "Hassibi, Babak" }, { "name": { "family": "Elachi", "given": "Charles" }, "id": "Elachi-C", "role": "member", "display_name": "Elachi, Charles" }, { "name": { "family": "Weinreb", "given": "Sander" }, "id": "Weinreb-S", "role": "member", "display_name": "Weinreb, Sander" } ], "option_major": [ "eleceng" ], "doi": "10.7907/25DP-J474", "abstract": "Abstract In the past decade, there has been a revolution in radio-astronomy signal processing. High bandwidth receivers coupled with fast ADCs have enabled the collection of tremendous instantaneous bandwidth, but streaming computational resources are struggling to catch up and serve these new capabilities. As a consequence, there is a need for novel signal processing algorithms capable of maximizing these resources. This thesis responds to the demand by presenting FPGA implementations of a Polyphase Filter Bank which are an order of magnitude more efficient than previous algorithms while exhibiting similar noise performance. These algorithms are showcased together alongside a broadband RF front-end in Starburst: a 5 GHz instantaneous bandwidth two-element interferometer, the first broadband digital sideband separating astronomical interferometer.\u00a0 Starburst technology has been applied to three instruments to date.
\r\n\r\nAbstract Wielding tremendous computational power and precisely calibrated hardware, low frequency radio telescope arrays have potential greatly exceeding their current applications.\u00a0 This thesis presents new modes for low frequency radio-telescopes, dramatically extending their original capabilities.\u00a0 A microsecond-scale time/frequency mode empowered the Owens Valley Long Wavelength Array to inspect not just the radio sky by enabling the testing of novel imaging techniques and detecting overhead beacon satellites, but also the terrestrial neighborhood, allowing for the characterization and mitigation of nearby sources of radio frequency interference (RFI).\u00a0 This characterization led to insights prompting a nanosecond-scale observing mode to be developed, opening new avenues in high energy astrophysics, specifically related to the radio frequency detection of ultra-high energy cosmic rays and neutrinos.
\r\n\r\nAbstract Measurement of the flux spectrum, composition, and origin of the highest energy cosmic ray events is a lofty goal in high energy astrophysics. One of the most powerful new windows has been the detection of associated extensive air showers at radio frequencies. However, all current ground-based systems must trigger off an expensive and insensitive external source such as particle detectors - making detection of the rare, high energy events uneconomical.\u00a0 Attempts to make a direct detection in radio-only data have been unsuccessful despite numerous efforts. The problem is even more severe in the case of radio detection of ultra-high energy neutrino events, which cannot rely on in-situ particle detectors as a triggering mechanism. This thesis combines the aforementioned nanosecond-scale observing mode with real-time, on-FPGA RFI mitigation and sophisticated offline post-processing.\u00a0 The resulting system has produced the first successful ground based detection of cosmic rays using only radio instruments. Design and measurements of cosmic ray detections are discussed, as well as recommendations for future cosmic ray experiments.\u00a0 The presented future designs allow for another order of magnitude improvement in both sensitivity and output data-rate, paving the way for the economical ground-based detection of the highest energy neutrinos.
" }, { "name": "Villadsen, Jacqueline Rose", "degree": "PhD", "year": "2017", "title": "The Search for Stellar Coronal Mass Ejections", "advisor": "Hallinan, Gregg W.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02022017-141014631", "creators": [ { "name": { "family": "Villadsen", "given": "Jacqueline Rose" }, "id": "Villadsen-Jacqueline-Rose", "orcid": "0000-0003-3924-243X", "display_name": "Villadsen, Jacqueline Rose" } ], "advisors": [ { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "advisor", "display_name": "Hallinan, Gregg W." } ], "committee": [ { "name": { "family": "Hillenbrand", "given": "Lynne A." }, "id": "Hillenbrand-L-A", "role": "chair", "display_name": "Hillenbrand, Lynne A." }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "orcid": "0000-0002-9656-4032", "role": "member", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Pearson", "given": "Timothy J." }, "id": "Pearson-T-J", "orcid": "0000-0001-5213-6231", "role": "member", "display_name": "Pearson, Timothy J." }, { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "orcid": "0000-0001-5390-8563", "role": "member", "display_name": "Kulkarni, Shrinivas R." }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "member", "display_name": "Hallinan, Gregg W." } ], "option_major": [ "astrophys" ], "doi": "10.7907/Z9P55KGB", "abstract": "Coronal mass ejections (CMEs) may dramatically impact habitability and atmospheric composition of planets around magnetically active stars, including young solar analogs and many M dwarfs. Theoretical predictions of such effects are limited by the lack of observations of stellar CMEs. This thesis addresses this gap through a search for the spectral and spatial radio signatures of CMEs on active M dwarfs.
\r\n\r\nSolar CMEs produce radio bursts with a distinctive spectral signature, narrow-band plasma emission that drifts to lower frequency as a CME expands outward. To search for analogous events on nearby stars, I worked on system design, software, and commissioning for the Starburst project, a wideband single-baseline radio interferometry backend dedicated to stellar observations. In addition, I led a survey of nearby active M dwarfs with the Karl G. Jansky Very Large Array (VLA), detecting coherent radio bursts in 13 out of 23 epochs, over a total of 58 hours. This survey's ultra-wide bandwidth (0.23-6.0 GHz) dynamic spectroscopy, unprecedented for stellar observations, revealed diverse behavior in the time-frequency plane. Flare star UV Ceti produced complex, luminous events reminiscent of brown dwarf aurorae; AD Leo sustained long-duration, intense, narrow-band \"storms\"; and YZ CMi emitted a burst with substructure with rapid frequency drift, resembling solar Type III bursts, which are attributed to electrons moving at speeds of order 10% of the speed of light.
\r\n\r\nTo search for the spatial signature of CMEs, I led 8.5-GHz observations with the Very Long Baseline Array simultaneous to 24 hours of the VLA survey. This program detected non-thermal continuum emission from the stars in all epochs, as well as continuum flares on AD Leo and coherent bursts on UV Ceti, enabling measurement of the spatial offset between flaring and quiescent emission.
\r\n\r\nThese observations demonstrate the diversity of stellar transients that can be expected in time-domain radio surveys, especially with the advent of large low-frequency radio telescopes. Wide bandwidth radio dynamic spectroscopy, complemented by high-resolution imaging of the radio corona, is a powerful technique for detecting stellar eruptions and characterizing dynamic processes in the stellar corona.
" }, { "name": "Manohar, Swarnima", "degree": "PhD", "year": "2016", "title": "Lurking in ULIRGs: Molecular Gas in local Merging Galaxies", "advisor": "Scoville, Nicholas Zabriskie", "url": "https://resolver.caltech.edu/CaltechTHESIS:03042016-144127692", "creators": [ { "name": { "family": "Manohar", "given": "Swarnima" }, "id": "Manohar-Swarnima", "orcid": "0000-0002-3506-566X", "display_name": "Manohar, Swarnima" } ], "advisors": [ { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "orcid": "0000-0002-0438-3323", "role": "advisor", "display_name": "Scoville, Nicholas Zabriskie" } ], "committee": [ { "name": { "family": "Sargent", "given": "Anneila Isabel" }, "id": "Sargent-A-I", "orcid": "0000-0002-4633-5098", "role": "chair", "display_name": "Sargent, Anneila Isabel" }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Hopkins", "given": "Philip F." }, "id": "Hopkins-P-F", "orcid": "0000-0003-3729-1684", "role": "member", "display_name": "Hopkins, Philip F." }, { "name": { "family": "Mawet", "given": "Dimitri" }, "id": "Mawet-D", "orcid": "0000-0002-8895-4735", "role": "member", "display_name": "Mawet, Dimitri" }, { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "orcid": "0000-0002-0438-3323", "role": "member", "display_name": "Scoville, Nicholas Zabriskie" } ], "option_major": [ "astrophys" ], "doi": "10.7907/Z9T72FDK", "abstract": "Mergers and interacting galaxies are pivotal to the evolution of galaxies in the universe. They are the sites of prodigious star formation and key to understanding the starburst processes: the physical and chemical properties and the dynamics of the molecular gas. ULIRGs or Ultraluminous Infrared Galaxies are a result of many of these mergers. They host extreme starbursts, AGNs, and mergers. They are the perfect laboratory to probe the connection between starbursts, black hole accretion and mergers and to further our understanding of star formation and merging.
\r\n\r\nNGC 6240 and Arp 220 can be considered the founding members of this very active class of objects. They are in different stages of merging and hence are excellent case studies to further our understanding about the merging process. We have imaged the dense star-forming regions of these galaxies at sub-arcsec resolution with CARMA C and B Configurations (2\" and 0.5 - 0.8\"). Multi-band imaging allows excitation analysis of HCN, HCO+, HNC, and CS along with CO transitions to constrain the properties of the gas. Our dataset is unique in that we have observed these lines at similar resolutions and high sensitivity which can be used to derive line ratios of faint high excitation lines.
\r\n\r\nArp 220 has not had confirmed X-ray AGN detections for either nuclei. However, our observations indicate HCN/HNC ratios consistent with the chemistry of X-ray Dominated Regions (XDRs) -- a likely symptom of AGN. We calculated the molecular Hydrogen densities using each of the molecular species and conclude that assuming abundances of HNC and HCO+ similar to those in galactic sources are incorrect in the case of ULIRGs. The physical conditions in the dense molecular gas in ULIRGs alter these abundances. The derived H2 volume densities are ~ 5 x 104 cm-3 in both Arp 220 nuclei and ~ 104 cm-3 in NGC 6240.
" }, { "name": "Mooley, Kunal Prakash", "degree": "PhD", "year": "2015", "title": "Exploring the Dynamic Radio Sky: The Search for Slow Transients with the VLA", "advisor": "Kulkarni, Shrinivas R.; Hallinan, Gregg W.; Frail, Dale A.; Myers, Steven T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03222015-185636984", "creators": [ { "name": { "family": "Mooley", "given": "Kunal Prakash" }, "id": "Mooley-Kunal-Prakash", "orcid": "0000-0002-2557-5180", "display_name": "Mooley, Kunal Prakash" } ], "advisors": [ { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "orcid": "0000-0001-5390-8563", "role": "co-advisor", "display_name": "Kulkarni, Shrinivas R." }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "co-advisor", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "Frail", "given": "Dale A." }, "id": "Frail-D-A", "role": "co-advisor", "display_name": "Frail, Dale A." }, { "name": { "family": "Myers", "given": "Steven T." }, "id": "Myers-Steven-Theodore", "role": "co-advisor", "display_name": "Myers, Steven T." } ], "committee": [ { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "orcid": "0000-0002-9656-4032", "role": "chair", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Hallinan", "given": "Gregg W." }, "id": "Hallinan-G-W", "orcid": "0000-0002-7083-4049", "role": "member", "display_name": "Hallinan, Gregg W." }, { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "orcid": "0000-0001-5390-8563", "role": "member", "display_name": "Kulkarni, Shrinivas R." }, { "name": { "family": "Hillenbrand", "given": "Lynne A." }, "id": "Hillenbrand-L-A", "orcid": "0000-0001-8638-0320", "role": "member", "display_name": "Hillenbrand, Lynne A." }, { "name": { "family": "Myers", "given": "Steven T." }, "id": "Myers-Steven-Theodore", "role": "member", "display_name": "Myers, Steven T." } ], "option_major": [ "astrophys" ], "abstract": "While synoptic surveys in the optical and at high energies have revealed a rich discovery phase space of slow transients, a similar yield is still awaited in the radio. Majority of the past blind surveys, carried out with radio interferometers, have suffered from a low yield of slow transients, ambiguous transient classifications, and contamination by false positives. The newly-refurbished Karl G. Jansky Array (Jansky VLA) offers wider bandwidths for accurate RFI excision as well as substantially-improved sensitivity and survey speed compared with the old VLA. The Jansky VLA thus eliminates the pitfalls of interferometric transient search by facilitating sensitive, wide-field, and near-real-time radio surveys and enabling a systematic exploration of the dynamic radio sky. This thesis aims at carrying out blind Jansky VLA surveys for characterizing the radio variable and transient sources at frequencies of a few GHz and on timescales between days and years. Through joint radio and optical surveys, the thesis addresses outstanding questions pertaining to the rates of slow radio transients (e.g. radio supernovae, tidal disruption events, binary neutron star mergers, stellar flares, etc.), the false-positive foreground relevant for the radio and optical counterpart searches of gravitational wave sources, and the beaming factor of gamma-ray bursts. The need for rapid processing of the Jansky VLA data and near-real-time radio transient search has enabled the development of state-of-the-art software infrastructure. This thesis has successfully demonstrated the Jansky VLA as a powerful transient search instrument, and it serves as a pathfinder for the transient surveys planned for the SKA-mid pathfinder facilities, viz. ASKAP, MeerKAT, and WSRT/Apertif." }, { "name": "Stevenson, Matthew Alan", "degree": "PhD", "year": "2014", "title": "Observational and Theoretical Advances in Cosmological Foreground Emission", "advisor": "Readhead, Anthony C. S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:09292013-182521898", "creators": [ { "name": { "family": "Stevenson", "given": "Matthew Alan" }, "id": "Stevenson-Matthew-Alan", "display_name": "Stevenson, Matthew Alan" } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." } ], "committee": [ { "name": { "family": "Hirata", "given": "Christopher M." }, "id": "Hirata-C-M", "orcid": "0000-0002-2951-4932", "role": "chair", "display_name": "Hirata, Christopher M." }, { "name": { "family": "Golwala", "given": "Sunil" }, "id": "Golwala-S-R", "orcid": "0000-0002-1098-7174", "role": "member", "display_name": "Golwala, Sunil" }, { "name": { "family": "Hillenbrand", "given": "Lynne A." }, "id": "Hillenbrand-L-A", "role": "member", "display_name": "Hillenbrand, Lynne A." }, { "name": { "family": "Pearson", "given": "Timothy J." }, "id": "Pearson-T-J", "orcid": "0000-0001-5213-6231", "role": "member", "display_name": "Pearson, Timothy J." }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "orcid": "0000-0002-0438-3323", "role": "member", "display_name": "Scoville, Nicholas Zabriskie" } ], "option_major": [ "astrophys" ], "abstract": "Observational and theoretical work towards the separation of foreground emission from the cosmic microwave background is described. The bulk of this work is in the design, construction, and commissioning of the C-Band All-Sky Survey (C-BASS), an experiment to produce a template of the Milky Way Galaxy's polarized synchrotron emission. Theoretical work is the derivation of an analytical approximation to the emission spectrum of spinning dust grains.
\r\n\r\nThe performance of the C-BASS experiment is demonstrated through a preliminary, deep survey of the North Celestial Pole region. A comparison to multiwavelength data is performed, and the thermal and systematic noise properties of the experiment are explored. The systematic noise has been minimized through careful data processing algorithms, implemented both in the experiment's Field Programmable Gate Array (FPGA) based digital backend and in the data analysis pipeline. Detailed descriptions of these algorithms are presented.
\r\n\r\nThe analytical function of spinning dust emission is derived through the application of careful approximations, with each step tested against numerical calculations. This work is intended for use in the parameterized separation of cosmological foreground components and as a framework for interpreting and comparing the variety of anomalous microwave emission observations.
\r\n" }, { "name": "Max-Moerbeck Astudillo, Walter Kennerth", "degree": "PhD", "year": "2013", "title": "The Relationship Between the Radio and Gamma-Ray Emission of Blazars", "advisor": "Readhead, Anthony C. S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302013-225100503", "creators": [ { "name": { "family": "Max-Moerbeck Astudillo", "given": "Walter Kennerth" }, "id": "Max-Moerbeck-Astudillo-Walter-Kennerth", "display_name": "Max-Moerbeck Astudillo, Walter Kennerth" } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." } ], "committee": [ { "name": { "family": "Cohen", "given": "Judith G." }, "id": "Cohen-J-G", "orcid": "0000-0002-8039-4673", "role": "chair", "display_name": "Cohen, Judith G." }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "orcid": "0000-0001-5390-8563", "role": "member", "display_name": "Kulkarni, Shrinivas R." }, { "name": { "family": "Hirata", "given": "Christopher M." }, "id": "Hirata-C-M", "orcid": "0000-0002-2951-4932", "role": "member", "display_name": "Hirata, Christopher M." }, { "name": { "family": "Djorgovski", "given": "George" }, "id": "Djorgovski-G", "orcid": "0000-0002-0603-3087", "role": "member", "display_name": "Djorgovski, George" } ], "option_major": [ "astrophys" ], "doi": "10.7907/ZX5X-V114", "abstract": "Blazars are active galaxies with a jet closely oriented to our line of sight. They are powerful, variable emitters from radio to gamma-ray wavelengths. Although the general picture of synchrotron emission at low energies and inverse Compton at high energies is well established, important aspects of blazars are not well understood. In particular, the location of the gamma-ray emission region is not clearly established, with some theories favoring a location close to the central engine, while others place it at parsec scales in the radio jet.
\r\n\r\nWe developed a program to locate the gamma-ray emission site in blazars, through the study of correlated variations between their gamma-ray and radio-wave emission. Correlated variations are expected when there is a relation between emission processes at both bands, while delays tell us about the relative location of their energy generation zones. Monitoring at 15 GHz using the Owens Valley Radio Observatory 40 meter telescope started in mid-2007. The program monitors 1593 blazars twice per week, including all blazars detected by the Fermi Gamma-ray Space Telescope (Fermi) north of -20 degrees declination. This program complements the continuous monitoring of gamma-rays by Fermi.
\r\n\r\nThree year long gamma-ray light curves for bright Fermi blazars are cross-correlated with four years of radio monitoring. The significance of cross-correlation peaks is investigated using simulations that account for the uneven sampling and noise properties of the light curves, which are modeled as red-noise processes with a simple power-law power spectral density. We found that out of 86 sources with high quality data, only three show significant correlations (AO 0235+164, B2 2308+34 and PKS 1502+106). Additionally, we find a significant correlation for Mrk 421 when including the strong gamma-ray/radio flare of late 2012. In all four cases radio variations lag gamma-ray variations, suggesting that the gamma-ray emission originates upstream of the radio emission. For PKS 1502+106 we locate the gamma-ray emission site parsecs away from the central engine, thus disfavoring the model of Blandford and Levinson (1995), while other cases are inconclusive. These findings show that continuous monitoring over long time periods is required to understand the cross-correlation between gamma-ray and radio-wave variability in most blazars.
" }, { "name": "P\u00e9rez Mu\u00f1oz, Laura Mar\u00eda", "degree": "PhD", "year": "2013", "title": "Grain Growth in Protoplanetary Disks", "advisor": "Carpenter, John M.; Sargent, Anneila Isabel", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302013-223659579", "creators": [ { "name": { "family": "P\u00e9rez Mu\u00f1oz", "given": "Laura Mar\u00eda" }, "id": "Perez-Munoz-Laura-Mar\u00eda", "display_name": "P\u00e9rez Mu\u00f1oz, Laura Mar\u00eda" } ], "advisors": [ { "name": { "family": "Carpenter", "given": "John M." }, "id": "Carpenter-J-M", "orcid": "0000-0003-2251-0602", "role": "advisor", "display_name": "Carpenter, John M." }, { "name": { "family": "Sargent", "given": "Anneila Isabel" }, "id": "Sargent-A-I", "orcid": "0000-0002-4633-5098", "role": "advisor", "display_name": "Sargent, Anneila Isabel" } ], "committee": [ { "name": { "family": "Hirata", "given": "Christopher M." }, "id": "Hirata-C-M", "orcid": "0000-0002-2951-4932", "role": "chair", "display_name": "Hirata, Christopher M." }, { "name": { "family": "Carpenter", "given": "John M." }, "id": "Carpenter-J-M", "orcid": "0000-0003-2251-0602", "role": "member", "display_name": "Carpenter, John M." }, { "name": { "family": "Sargent", "given": "Anneila Isabel" }, "id": "Sargent-A-I", "orcid": "0000-0002-4633-5098", "role": "member", "display_name": "Sargent, Anneila Isabel" }, { "name": { "family": "Hillenbrand", "given": "Lynne A." }, "id": "Hillenbrand-L-A", "role": "member", "display_name": "Hillenbrand, Lynne A." }, { "name": { "family": "Johnson", "given": "John A." }, "id": "Johnson-J-A", "role": "member", "display_name": "Johnson, John A." }, { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "orcid": "0000-0001-5390-8563", "role": "member", "display_name": "Kulkarni, Shrinivas R." } ], "option_major": [ "astrophys" ], "doi": "10.7907/1BJC-4G54", "abstract": "The majority of young, low-mass stars are surrounded by optically thick accretion disks. These circumstellar disks provide large reservoirs of gas and dust that will eventually be transformed into planetary systems. Theory and observations suggest that the earliest stage toward planet formation in a protoplanetary disk is the growth of particles, from sub-micron-sized grains to centimeter- sized pebbles. Theory indicates that small interstellar grains are well coupled into the gas and are incorporated to the disk during the proto-stellar collapse. These dust particles settle toward the disk mid-plane and simultaneously grow through collisional coagulation in a very short timescale. Observationally, grain growth can be inferred by measuring the spectral energy distribution at long wavelengths, which traces the continuum dust emission spectrum and hence the dust opacity. Several observational studies have indicated that the dust component in protoplanetary disks has evolved as compared to interstellar medium dust particles, suggesting at least 4 orders of magnitude in particle- size growth. However, the limited angular resolution and poor sensitivity of previous observations has not allowed for further exploration of this astrophysical process.
\r\n\r\nAs part of my thesis, I embarked in an observational program to search for evidence of radial variations in the dust properties across a protoplanetary disk, which may be indicative of grain growth. By making use of high angular resolution observations obtained with CARMA, VLA, and SMA, I searched for radial variations in the dust opacity inside protoplanetary disks. These observations span more than an order of magnitude in wavelength (from sub-millimeter to centimeter wavelengths) and attain spatial resolutions down to 20 AU. I characterized the radial distribution of the circumstellar material and constrained radial variations of the dust opacity spectral index, which may originate from particle growth in these circumstellar disks. Furthermore, I compared these observational constraints with simple physical models of grain evolution that include collisional coagulation, fragmentation, and the interaction of these grains with the gaseous disk (the radial drift problem). For the parameters explored, these observational constraints are in agreement with a population of grains limited in size by radial drift. Finally, I also discuss future endeavors with forthcoming ALMA observations.
" }, { "name": "Corder, Stuartt Allan", "degree": "PhD", "year": "2009", "title": "Optimizing Image Fidelity with Arrays", "advisor": "Sargent, Anneila Isabel", "url": "https://resolver.caltech.edu/CaltechETD:etd-10172008-054754", "creators": [ { "name": { "family": "Corder", "given": "Stuartt Allan" }, "id": "Corder-Stuartt-Allan", "display_name": "Corder, Stuartt Allan" } ], "advisors": [ { "name": { "family": "Sargent", "given": "Anneila Isabel" }, "id": "Sargent-A-I", "role": "advisor", "display_name": "Sargent, Anneila Isabel" } ], "committee": [ { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "role": "chair", "display_name": "Blake, Geoffrey A." }, { "name": { "family": "Sargent", "given": "Anneila Isabel" }, "id": "Sargent-A-I", "role": "member", "display_name": "Sargent, Anneila Isabel" }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "role": "member", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Carpenter", "given": "John M." }, "id": "Carpenter-J-M", "role": "member", "display_name": "Carpenter, John M." }, { "name": { "family": "Wright", "given": "Melvyn" }, "id": "Wright-M", "role": "member", "display_name": "Wright, Melvyn" }, { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "role": "member", "display_name": "Kulkarni, Shrinivas R." } ], "option_major": [ "astrophys" ], "doi": "10.7907/Q7H2-2P58", "abstract": "Through simulations, I have investigated the limitations imposed upon the image fidelity of interferometric observations by primary beam errors. Significant antenna surface and pointing errors lead to the greatest reduction in fidelity for most cases, but, when present, imaginary beam components dominate the degradation. Beam errors were addressed by optimizing the antenna surfaces and aligning the optics and then determining baseline based primary beams. Methods for applying these measured patterns to actual data were discussed. Pointing errors were reduced by improving the fit to the pointing model. Further reduction was achieved by integrating the use of optical pointing observations into standard radio observing. The greatest benefit was seen during daytime observations, but general reduction in pointing error was seen.
\r\n\r\nThe dense uv-coverage of the Combined Array for Research in Millimeter-wave Astronomy (CARMA) coupled with the techniques described above make it an ideal instrument for imaging extended regions with high fidelity. The NGC 7538 star-forming cloud contains dense peaks, many high-mass stars and associated accretion disks, and multiple outflows. I obtained CARMA images at the requisite fidelity, employing the above techniques. These mosaiced, spectral-line, and 3-mm band continuum observations provide a clearer picture of the bulk morphology of the region and the fine-scale structures within it than has hitherto been possible. For the first time in the region, infall signatures were found towards two sources, allowing comparison of the infall and outflow mass and verifying that significant accretion (>10\u22124M\u2299 yr\u22121) continues well into the stage where a massive protostar has formed. One of the sources, NGC 7538IRS1, shows one of the few definitive signatures of an inverse PCygni profile towards a massive protostar. Three outflows were found centered on sources that are separated by 10,000-20,000 AU in projection. The calculated energy injection rate provides constraints for models of outflow feedback. The NGC 7538 results demonstrate clearly the capability of CARMA to provide high quality images over wide-fields and the benefits of the techniques I developed. While work to improve CARMA image fidelity continues, the program described here lays the groundwork and should help guide further enhancements of image fidelity at CARMA and at other radio facilities.
\r\n" }, { "name": "Christopher, Micol Huw", "degree": "PhD", "year": "2008", "title": "Young, Massive Star Clusters in the Antennae", "advisor": "Scoville, Nicholas Zabriskie", "url": "https://resolver.caltech.edu/CaltechETD:etd-05152008-141502", "creators": [ { "name": { "family": "Christopher", "given": "Micol Huw" }, "id": "Christopher-Micol-Huw", "display_name": "Christopher, Micol Huw" } ], "advisors": [ { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "orcid": "0000-0002-0438-3323", "role": "advisor", "display_name": "Scoville, Nicholas Zabriskie" } ], "committee": [ { "name": { "family": "Hillenbrand", "given": "Lynne A." }, "id": "Hillenbrand-L-A", "role": "chair", "display_name": "Hillenbrand, Lynne A." }, { "name": { "family": "Schweizer", "given": "Francois" }, "id": "Schweizer-F", "role": "member", "display_name": "Schweizer, Francois" }, { "name": { "family": "Cohen", "given": "Judith G." }, "id": "Cohen-J-G", "orcid": "0000-0002-8039-4673", "role": "member", "display_name": "Cohen, Judith G." }, { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "orcid": "0000-0002-0438-3323", "role": "member", "display_name": "Scoville, Nicholas Zabriskie" }, { "name": { "family": "Ellis", "given": "Richard S." }, "id": "Ellis-R-S", "role": "member", "display_name": "Ellis, Richard S." } ], "option_major": [ "astrophys" ], "doi": "10.7907/QP4P-SD67", "abstract": "While massive star clusters have been detected in almost every galaxy with appreciable star formation, they are most prevalent in interacting and merging galaxies. As many as 95% of these clusters will ultimately be disrupted, often in the first 10 Myr, but those clusters that do survive may be the progenitors of globular clusters. Many questions exist regarding these massive clusters and the processes that lead to their formation and disruption, including the uniformity of these processes within a galaxy and between galaxies with different degrees of cluster formation (e.g., quiescent spirals, starbursts, and merging systems). To address these questions, we present a detailed spectroscopic survey of young, massive star clusters in the Antennae, one of the best examples of cluster formation in a merging galaxy.
\r\n\r\nUsing near-infrared imaging, we selected a sample of 117 clusters to observe with a combination of near-infrared and optical spectroscopy at the W.M. Keck Observatory. These clusters were chosen to sample the major star-forming regions within the Antennae. This is the largest spectroscopic survey of young massive star clusters in any merging galaxy.
\r\n\r\nComparing the equivalent widths of hydrogen recombination lines and CO absorption bandheads to the population synthesis models of Starburst99, we measure the age of each cluster. More than half of the clusters show the simultaneous presence of hydrogen recombination lines and CO bandheads, which is not predicted by an instantaneous burst model of cluster formation. We determine that cluster formation is better modeled by a 5 Myr duration constant rate burst of star formation, which we apply to our cluster measurements. We find the vast majority of clusters have ages between 7 and 12 Myr, with a few younger clusters. Comparing cluster ages with predictions of the temporal evolution of cluster luminosity, we find the lack of older (>12 Myr) clusters (and to a lesser extent younger (<7 Myr) clusters) is not a selection effect but a true deficit. Variation in cluster ages exists with location in the Antennae, with the youngest clusters found in the overlap region where the disks of the two galaxies coincide. We interpret these age variations as an indication that cluster disruption rates differ by location within the Antennae.
\r\n\r\nCluster masses are measured by comparing the extinction-corrected K-band luminosity with model luminosity predictions. We find most cluster masses are between 105 and 106 M\u2609 with a median cluster mass around 3.5 x 105 M\u2609. Substantial variation exists in masses between different regions, with the overlap region having the most massive clusters on average. These mass differences can be interpreted as size-of-sample effects and our results are consistent with a uniform cluster initial mass function throughout the Antennae.
\r\n\r\nImproved spatial resolution CO (1-0) observations of the Antennae show that younger clusters coincide with areas of enhanced molecular gas concentration and, not surprisingly, also have on average higher extinctions. From two metallicity tracers, we find cluster metallicities consistent with solar values. Based on CO bandhead and SiI equivalent widths in the near-infrared spectra, we uncover strong evidence of a substantial population of M2--M4 supergiants in many of the older clusters.
\r\n" }, { "name": "Enoch, Melissa Lanae", "degree": "PhD", "year": "2008", "title": "Molecular Clouds and Star Formation: A Multiwavelength Study of Perseus, Serpens, and Ophiuchus", "advisor": "Carpenter, John M.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06292007-134316", "creators": [ { "name": { "family": "Enoch", "given": "Melissa Lanae" }, "id": "Enoch-Melissa-Lanae", "display_name": "Enoch, Melissa Lanae" } ], "advisors": [ { "name": { "family": "Carpenter", "given": "John M." }, "id": "Carpenter-J-M", "role": "advisor", "display_name": "Carpenter, John M." } ], "committee": [ { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "role": "chair", "display_name": "Scoville, Nicholas Zabriskie" }, { "name": { "family": "Sargent", "given": "Anneila Isabel" }, "id": "Sargent-A-I", "role": "member", "display_name": "Sargent, Anneila Isabel" }, { "name": { "family": "Carpenter", "given": "John M." }, "id": "Carpenter-J-M", "role": "member", "display_name": "Carpenter, John M." }, { "name": { "family": "Sari", "given": "Re'em" }, "id": "Sari-R", "role": "member", "display_name": "Sari, Re'em" }, { "name": { "family": "Golwala", "given": "Sunil" }, "id": "Golwala-S-R", "role": "member", "display_name": "Golwala, Sunil" } ], "option_major": [ "astrophys" ], "doi": "10.7907/25QK-5K72", "abstract": "In this thesis I utilize large-scale millimeter and mid- to far-infrared surveys to address a number of outstanding questions regarding the formation of low mass stars in molecular clouds. Continuum \u03bb = 1.1 mm maps completed with Bolocam at a resolution of 31\" cover the largest areas observed to date at millimeter or submillimeter wavelengths in three molecular clouds: 7.5 deg\u00b2 in Perseus (140 pc\u00b2 at the adopted distance of d = 250 pc), 10.8 deg\u00b2 (50 pc\u00b2 at d = 125 pc) in Ophiuchus, and 1.5 deg\u00b2 (30 pc\u00b2 at d = 125 pc) in Serpens. These surveys are sensitive to dense substructures with mean density n \u2273 2 - 3 x 10\u2074 cm\u207b\u00b3. A total of 122 cores are detected in Perseus, 44 in Ophiuchus, and 35 in Serpens above mass detection limits of 0.1 - 0.2 Msun. Combining with Spitzer mid- and far-infrared maps from the c2d Legacy program provides wavelength coverage from \u03bb = 1.25-1100 \u03bcm, and enables the assembly of an unbiased, complete sample of the youngest star forming objects in three environments. This sample includes 108 prestellar cores, 43 Class 0 sources and 94 Class I sources.
\r\n\r\nThe approximately equal number of starless cores and embedded protostars in each cloud implies a starless core lifetime of 2 - 4 x 10\u2075 yr, only a few free-fall timescales. This timescale, considerably shorter than the timescale predicted by the classic scenario of magnetic field support in which core evolution is moderated by ambipolar diffusion, suggests that turbulence is the dominant process controlling the formation and evolution of dense cores. However, dense cores in all three clouds are found only at high cloud column densities, where AV\u2273 7 mag, and the fraction of cloud mass in these cores is less than 10%, indicating that magnetic fields must play some role as well. Measured angular deconvolved sizes of the majority of starless cores are consistent with relatively flattened radial density profiles, or with Bonnor-Ebert spheres. The prestellar core mass distribution (CMD) has a slope of \u03b1 = -2.5 \u00b1 0.2 for M > 0.8 Msun, remarkably similar to recent measurements of the slope of the stellar initial mass function: \u03b1 = -2.3 to -2.8. While this result does not rule out the importance of feedback or competitive accretion, it provides support for the hypothesis that stellar masses are determined during the core formation process.
\r\n\r\nThe lifetime of the Class 0 phase is estimated to be 1 - 2 x 10\u2075 yr in Perseus and Serpens, or approximately half that of the Class I phase, arguing against a very rapid early accretion phase. In Ophiuchus the fraction of Class 0 sources is much smaller, consistent with previous measurements of a short (~ 10\u2074 yr) Class 0 phase in that cloud. A large population of low luminosity Class I sources that cannot be explained by constant or monotonically decreasing accretion rates is observed in each cloud. This result strongly suggest that accretion during the Class I phase is episodic, with sources spending approximately 25% of the Class I lifetime in a quiescent state.
\r\n\r\nFinally, I investigate the environmental dependence of star formation by comparing the dense core populations of the three clouds. Cores are found at considerably higher cloud column densities in Ophiuchus than in Perseus or Serpens; more than 75% of cores occur at visual extinctions of AV\u2273 8 mag in Perseus, AV\u2273 15 mag in Serpens, and AV\u2273 20 - 23 mag in Ophiuchus. Cloud CMDs are well characterized by power-law fits above their empirically derived 50% completeness limits, resulting in slopes of \u03b1 = -2.1 \u00b1 0.1 in Perseus, \u03b1 = -2.1 \u00b1 0.3 in Ophiuchus, and \u03b1 = -1.6 \u00b1 0.2 in Serpens. Measured slopes for Perseus and Ophiuchus broadly agree with turbulent fragmentation, but the relative shapes of the observed cloud CMDs are inconsistent with detailed simulations of the dependence of CMD shape on Mach number.
" }, { "name": "Sievers, Jonathan LeRoy", "degree": "PhD", "year": "2004", "title": "Data Analysis of and Results from Observations of the Cosmic Microwave Background with the Cosmic Background Imager", "advisor": "Readhead, Anthony C. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05282004-140350", "creators": [ { "name": { "family": "Sievers", "given": "Jonathan LeRoy" }, "id": "Sievers-Jonathan-LeRoy", "orcid": "0000-0001-6903-5074", "display_name": "Sievers, Jonathan LeRoy" } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." } ], "committee": [ { "name": { "family": "Steidel", "given": "Charles C." }, "id": "Steidel-C-C", "orcid": "0000-0002-4834-7260", "role": "chair", "display_name": "Steidel, Charles C." }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Kamionkowski", "given": "Marc P." }, "id": "Kamionkowski-M-P", "orcid": "0000-0001-7018-2055", "role": "member", "display_name": "Kamionkowski, Marc P." }, { "name": { "family": "Pearson", "given": "Timothy J." }, "id": "Pearson-T-J", "orcid": "0000-0001-5213-6231", "role": "member", "display_name": "Pearson, Timothy J." } ], "option_major": [ "astronomy" ], "doi": "10.7907/8706-VY52", "abstract": "We present results from observations of the Cosmic Microwave Background (CMB) with the Cosmic Background Imager (CBI), a sensitive 13-element interferometer located high in the Chilean Andes. We also discuss methods of analyzing the data from the CBI, including an improved way of measuring the true power spectrum using maximum likelihood estimation. This improved method leads to a saving of a factor of two in memory usage, and an increase in speed of order the number of points in the spectrum. The initial results are discussed, in which the fall-off in power at ell > 1000 (the \"damping tail\") was first observed. We also present the results from the first year of observations with the CBI, and discuss cosmological intepretations both alone and in concert with the results from other experiments. These provide tight constraints on cosmological parameters, including a Hubble constant of 69 +/- 4 km/s/Mpc, an age of the universe of 13.7 +/- 0.2 billion years, and a denisty of dark energy of 0.70 +/- 0.05 of the critical density of the universe. Finally, we discuss an alternate method of data compression, with great flexibility in what information is kept, while being computationally tractable. We then apply this method to the CBI data to constrain the potential emission from foreground contaminants contributing to the observed CMB radiation. We find that the data is consistent with zero foreground, with a maximum allowed foreground contribution between about 8% and 12% of the total signal (at an ell of 600 and frequency of 30 GHz), depending on the spectral index of foreground emission.\r\n" }, { "name": "Udomprasert, Patricia Simcoe", "degree": "PhD", "year": "2004", "title": "H\u2080 from Cosmic Background Imager Observations of the Sunyaev-Zel\u2019dovich Effect in Nearby Clusters.", "advisor": "Readhead, Anthony C. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05132004-184937", "creators": [ { "name": { "family": "Udomprasert", "given": "Patricia Simcoe" }, "id": "Udomprasert-Patricia-Simcoe", "display_name": "Udomprasert, Patricia Simcoe" } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." } ], "committee": [ { "name": { "family": "Lange", "given": "Andrew E." }, "id": "Lange-A-E", "role": "chair", "display_name": "Lange, Andrew E." }, { "name": { "family": "Blain", "given": "Andrew W." }, "id": "Blain-A-W", "role": "member", "display_name": "Blain, Andrew W." }, { "name": { "family": "Djorgovski", "given": "George" }, "id": "Djorgovski-G", "orcid": "0000-0002-0603-3087", "role": "member", "display_name": "Djorgovski, George" }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "orcid": "0000-0002-9656-4032", "role": "member", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." } ], "option_major": [ "astronomy" ], "doi": "10.7907/VR2Z-MP09", "abstract": "We present H\u2080 results from Cosmic Background Imager (CBI) observations of the Sunyaev-Zeldovich Effect (SZE) in 7 galaxy clusters, A85, A399, A401, A478, A754, A1651, and A2597. These observations are part of a program to study a complete, volume-limited sample of low-redshift (z < 0.1), X-ray selected clusters. Our focus on nearby objects allows us to study a well-defined, orientation unbiased sample, minimizing systematic errors due to cluster asphericity. We use density models derived from ROSAT imaging data and temperature measurements from ASCA and BeppoSAX spectral observations. We quantify in detail sources of error in our derivation of H\u2080, including calibration of the CBI data, density and temperature models from the X-ray data, Cosmic Microwave Background (CMB) primary anisotropy fluctuations, and residuals from radio point source subtraction. From these 7 clusters we obtain a result of Ho = 67+30-18(ran)+15-6(sys) km/s-1 Mpc-1 for an unweighted sample average. The respective quoted errors are random and systematic uncertainties at 68% confidence. The dominant source of error is confusion from intrinsic anisotropy fluctuations. We present results from simulations of an eigenmode weighting analysis that reduce the uncertainties due to CMB in h-1/2 by ~30%." }, { "name": "Cartwright, John Kenneth", "degree": "PhD", "year": "2003", "title": "A Limit on the Polarization of the Cosmic Microwave Background Radiation", "advisor": "Readhead, Anthony C. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-05292003-131234", "creators": [ { "name": { "family": "Cartwright", "given": "John Kenneth" }, "id": "Cartwright-John-Kenneth", "display_name": "Cartwright, John Kenneth" } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." } ], "committee": [ { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "orcid": "0000-0002-9656-4032", "role": "chair", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Lange", "given": "Andrew E." }, "id": "Lange-A-E", "role": "member", "display_name": "Lange, Andrew E." }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Zmuidzinas", "given": "Jonas" }, "id": "Zmuidzinas-J", "orcid": "0000-0002-3330-5439", "role": "member", "display_name": "Zmuidzinas, Jonas" }, { "name": { "family": "Padin", "given": "Stephen" }, "id": "Padin-Stephen", "orcid": "0009-0001-9993-4393", "role": "member", "display_name": "Padin, Stephen" } ], "option_major": [ "astronomy" ], "doi": "10.7907/D3CT-YV96", "abstract": "We describe polarization observations of the CMBR with the Cosmic Background Imager, a 13-element interferometer which operates in the 26-36 GHz band and is located on the Llano de Chajnantor in northern Chile. The array consists of 90 cm Cassegrain antennas mounted on a steerable platform which can be rotated about the optical axis to facilitate polarization observations. The CBI employs single-mode circularly polarized receivers and it samples multipoles from \u2113 ~ 400 to \u2113 ~ 4250. The instrumental polarization of the CBI was calibrated with 3C279, a bright polarized point source which was monitored with the VLA. Observations of two deep fields during the 2000 season yielded three limits (95% c.l.) for C\u2113EE under the assumption that C\u2113BB = 0: 7.0 \u00b5K (\u2113 = 603); 12.8 \u00b5K (\u2113 = 1144); and 25.1 \u00b5K (\u2113 = 2048). The low-\u2113 limit approaches the levels of fluctuations predicted by standard models.
\r\n\r\nThis thesis also entailed the design and implementation of several major components of the CBI signal chain including the downconverter, the noise calibration system, and the low noise HEMT amplifiers. We discuss the design and performance of these critical systems.
" }, { "name": "Baker, Andrew Jordan", "degree": "PhD", "year": "2000", "title": "Molecular Gas in Nearby Active Galactic Nuclei", "advisor": "Scoville, Nicholas Zabriskie", "url": "https://resolver.caltech.edu/CaltechETD:etd-09202008-104918", "creators": [ { "name": { "family": "Baker", "given": "Andrew Jordan" }, "id": "Baker-Andrew-Jordan", "orcid": "0000-0002-7892-396X", "display_name": "Baker, Andrew Jordan" } ], "advisors": [ { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "role": "advisor", "display_name": "Scoville, Nicholas Zabriskie" } ], "committee": [ { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "role": "chair", "display_name": "Scoville, Nicholas Zabriskie" }, { "name": { "family": "Neugebauer", "given": "Gerry" }, "id": "Neugebauer-G", "role": "member", "display_name": "Neugebauer, Gerry" }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "role": "member", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Sargent", "given": "Wallace L. W." }, "id": "Sargent-W-L-W", "role": "member", "display_name": "Sargent, Wallace L. W." }, { "name": { "family": "Steidel", "given": "Charles C." }, "id": "Steidel-C-C", "role": "member", "display_name": "Steidel, Charles C." } ], "option_major": [ "astronomy" ], "doi": "10.7907/c2qn-2b77", "abstract": "This thesis describes the distributions, physical conditions, and kinematics of the molecular gas in eight nearby galaxies whose Seyfert and LINER nuclei display broad H\u03b1 emission. We have mapped these systems at a linear resolution of ~ 100 pc in the CO(2-1) rotational transition, as well as at lower resolution in the CO(1-0) line, using the Owens Valley Radio Observatory millimeter array. Subsequent kinematical modelling allows us to improve on this angular resolution by exploiting our high effective velocity resolution; we simultaneously determine the radial emissivity profile of each line and the velocity field which the gas traces. Analysis of the molecular emission from individual objects reveals (1) massive concentrations of molecular gas (~ 10\u2079M\u2609) at small galactocentric radii (r \u2264 500 pc); (2) a pattern of high excitation at small radius, implied by variation in the ratio of CO (2-1) to CO(1-0) integrated intensities, which we attribute in part to the external heating of molecular clouds by energetic photons; (3) a high occurrence of nonaxisymmetric structures within 500 pc of the nucleus, including four gas bars; (4) evidence for episodic mass inflow along stellar bars outside 500 pc; and (5) apparent redirection of radio jets and ionizing photons from the nucleus by the molecular gas which they encounter. Our most striking discoveries are a dynamically decoupled secondary bar in the nucleus of NGC 7479, a mean integrated intensity ratio \u2265 1.85 in the nucleus of NGC 2681, and a warped molecular disk in the nucleus of NGC 1068.\r\n" }, { "name": "Grego, Laura", "degree": "PhD", "year": "1999", "title": "Galaxy cluster gas fractions from interferometric measurements of the Sunyaev-Zel'dovich effect", "advisor": "Carlstrom, John E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:08252010-152734353", "creators": [ { "name": { "family": "Grego", "given": "Laura" }, "id": "Grego-L", "display_name": "Grego, Laura" } ], "advisors": [ { "name": { "family": "Carlstrom", "given": "John E." }, "id": "Carlstrom-J-E", "role": "advisor", "display_name": "Carlstrom, John E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "physics" ], "doi": "10.7907/acvg-2168", "abstract": "Interferometric measurements of the Sunyaev-Zel'dovich effect toward 18 highly x-ray luminous galaxy clusters are presented. The observations were made using centimeter-wave receivers specifically constructed for these observations. The data were taken with the receivers mounted on the Owens Valley Radio Observatory and Berkeley-Illinois-Maryland Association millimeter arrays between 1994 and 1998. The interferometric data are used to determine the gas mass fraction in these clusters in a uniform method. The inteferometric data contain sufficient spatial information to derive models for the pressure distribution of the cluster gas. From these models, under the assumption that the gas is isothermal, the cluster gas masses are estimated and the total gravitating masses are inferred. The total gravitating mass measurement requires the additional assumption that the gas is in hydrostatic equilibrium with the cluster potential. The cluster gas temperatures are obtained from x-ray spectral observations or, in the few cases in which spectra were unavailable, estimated from x-ray luminosity-temperature relations in the literature. Since the experiment best measures the gas fraction within a fixed angular radius, the measured gas fractions are extrapolated to a fiducial radius, using a relation derived from published numerical simulations, to facilitate comparisons. The best estimate of the cluster gas fraction at \u03c4_(500), the radius at which the enclosed mean density is 500 times the critical density, is (0.071^(+0.010)_(-0.012))h^(-1)_(100) at 68% confidence. Under the assumption that clusters are fair samples of the universe, the mass composition in clusters at the virial radius should reflect the universal mass composition. The intracluster gas is the dominant component of a cluster's baryonic mass, and so the gas mass fraction is a good approximation of the baryon mass fraction. The baryon fraction in clusters, f_B, together with the universal baryon mass density, \u03a9_B, sets a limit on the universal mass density, in the standard cosmological paradigm: \u03a9_M = \u03a9_B/ f_B. The cluster gas fraction measurements presented here set an upper limit to the universal mass density: \u03a9_Mh_(100) \u2264 0.27^(+0.07)_(-0.06), at 68% confidence. We make our best estimate of the universal matter density, including with the gas fraction estimates of the baryonic mass contained in galaxies and the baryonic mass which failed to become bound during the cluster formation process: \u03a9_M = 0.29^(+0.08)_(-0.06) at 68% confidence for h = 0.7." }, { "name": "Leitch, Erik M.", "degree": "PhD", "year": "1998", "title": "A measurement of anisotropy in the microwave background on 7'-22' scales", "advisor": "Readhead, Anthony C. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08162006-081019", "creators": [ { "name": { "family": "Leitch", "given": "Erik M." }, "id": "Leitch-Erik-M", "display_name": "Leitch, Erik M." } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/DRVA-T966", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nA measurement of the anisotropy of the cosmic microwave background radiation (CMBR) at 7'-22' scales is described. Observations of 36 blank fields near the North Celestial Pole (NCP) were made at 31.7 and 14.5 GHz, using two High Electron Mobility Transistor (HEMT) amplified radiometers. These observations were conducted at the Owens Valley Radio Observatory from 1993-1996.\r\n\r\nWe detect a significant signal, with temperature spectral index consistent with emission from a combination of a steep-spectrum foreground ([beta] < -2) and CMBR ([...]). Multi-epoch VLA observations at 8 and 15 GHz allow removal of any discrete source contamination at 14.5 and 31.7 GHz. On the basis of low-frequency maps of the NCP, we can rule out emission with [beta] < -2.2. Although the foreground signal dominates at 14.5 GHz, the extracted CMBR component contributes nearly 90% of the variance at 31.7 GHz, yielding an rms fluctuation amplitude of [...], including calibration uncertainty and sample variance. In terms of the angular power spectrum [...] averaged over a range of multipoles [...], we have [...].\r\n\r\nThe extracted foreground component is found to correlate significantly with IRAS 100 [mu] m dust emission. Lack of H [alpha] emission near the NCP suggests that the foreground is either high-temperature thermal bremsstrahlung [...], flat spectrum synchrotron, or an exotic component of dust emission.\r\n" }, { "name": "Akeson, Rachel Lynn", "degree": "PhD", "year": "1997", "title": "Millimeter Interferometric Polarimetry of Magnetic Field Structure in Protostellar Condensations", "advisor": "Carlstrom, John E.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09172008-132123", "creators": [ { "name": { "family": "Akeson", "given": "Rachel Lynn" }, "id": "Akeson-Rachel-Lynn", "orcid": "0000-0001-9674-1564", "display_name": "Akeson, Rachel Lynn" } ], "advisors": [ { "name": { "family": "Carlstrom", "given": "John E." }, "id": "Carlstrom-J-E", "role": "advisor", "display_name": "Carlstrom, John E." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/RGCX-HK35", "abstract": "Images of the linearly polarized emission from magnetically aligned dust grains have been used to investigate the magnetic field structure in the dense environments of young stellar objects. These observations provide constraints for theoretical modeling on scales relevant to protostellar disks, envelopes and outflows. Adjustable reflecting polarizers were installed at the Owens Valley Radio Observatory millimeter array to allow observations of polarized emission.
\r\n\r\nPolarized emission was detected toward two young stellar objects NGC 1333/ IRAS 4A and IRAS 16293-2422. Both sources are highly embedded and considered among the youngest objects known. The strong sub-millimeter and millimeter fluxes indicate a large amount of circumstellar material which may correspond to the magnetically supported envelopes predicted by theoretical models. Toward IRAS 4A, the magnetic field direction implied by the polarization position angle is parallel to the bipolar molecular outflow. Radiative transfer models were calculated and the offset of the polarized emission toward red-shifted outflow is consistent with an hourglass field morphology in the envelope.
\r\n\r\nThe polarized emission toward IRAS 16293 is located between the two binary components. The magnetic field direction coincides with directions seen in one of the four outflow lobes. However, the field direction is perpendicular to the rotation axis of the circumbinary disk. Given the complicated outflow and circumbinary disk structure of the source, a simple model can not explain the implied magnetic field direction or the offset of the polarized emission from the total intensity.
\r\n\r\nObservations were also made of the Orion KL region, though no polarization was detected. The upper limit to the polarized emissions suggests that the decrease in polarization seen by single-dish surveys toward the high mass young stellar object IRc2, is not due to field tangling.
\r\n\r\nThe implications of significant polarized emission as detected in the envelopes of IRAS 4A and IRAS 16293 are considered for several alignment mechanisms. Alignment by paramagnetic relaxation of thermally rotating grains will not be efficient in these dense, warm regions, and some mechanism for suprathermal grain rotation may be necessary to explain the observations.
\r\n\r\nThese observations clearly demonstrate the power of interferometric millimeter polarimetry in the study of the role of magnetic fields in protostellar condensations.
\r\n" }, { "name": "Bryant, Peter M.", "degree": "PhD", "year": "1997", "title": "High-resolution observations of the molecular gas in luminous infrared galaxies", "advisor": "Scoville, Nicholas Zabriskie", "url": "https://resolver.caltech.edu/CaltechETD:etd-09202008-104546", "creators": [ { "name": { "family": "Bryant", "given": "Peter M." }, "id": "Bryant-P-M", "display_name": "Bryant, Peter M." } ], "advisors": [ { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "role": "advisor", "display_name": "Scoville, Nicholas Zabriskie" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/0rav-qq54", "abstract": "I have performed a high-resolution imaging survey of the molecular gas in seven luminous infrared galaxies using the Owens Valley millimeter array. This work has produced 2\"-resolution maps of the CO 1\u21920 emission. Further high-resolution data has been obtained for subsets of these galaxies in CO 2\u21921, HCN 1\u21920, HCO[superscript +] 1\u21920 and CS 1\u21920.\r\n\r\nThe CO maps reveal a systematic variation in the morphology of the molecular gas with the interaction state of the system. The three mergers with a single IR/radio nucleus show very bright and compact CO cores that peak at the stellar nucleus. The two mergers with double IR/radio nuclei also possess bright CO cores, but these peak roughly midway between the nuclei and show an extent nearly equal to the nuclear separation. In these objects, the gas cores of the individual merging galaxies appear to be coalescing while the stellar nuclei still remain distinct.\r\n\r\nBased on dynamical arguments, the Galactic conversion factor from CO luminosity to molecular gas mass is overestimating the gas mass in Mrk 231 by at least a factor of 3.6 and in NGC 6240 by at least a factor of 1.5. Nonetheless, the molecular gas likely dominates the nuclear gravitational potential. The probable cause of the severe overestimate in Mrk 231 is the high brightness temperature of the CO 1\u21920 emission (T[subscript b] > 34 K).\r\n\r\nStarbursts remain a viable explanation for the powerful output of luminous infrared galaxies. Upper limits to the free-free mm-wave continuum are used to constrain a starburst model from the literature, with the result that starbursts can reasonably explain all the systems studied here except perhaps Mrk 231. In several cases, though, they are required to be older than several 10[superscript 7] yr. Furthermore, the extreme mid-IR optical depths implied by the CO surface brightnesses confirm a prediction of the compact starburst model of Condon et al. (1991).\r\n\r\nThe trend of increasing L[subscript FIR]/L[subscript CO] ratio with increasing CO surface brightness is confirmed. The high concentrations of molecular gas thus appear intimately related to the high luminosities of these systems.\r\n\r\nThe CO/HCN ratio varies by an order of magnitude even in this small sample of luminous mergers, suggesting that the gas properties are dramatically variable.\r\n" }, { "name": "Putney, Angela", "degree": "PhD", "year": "1996", "title": "Magnetic white dwarf stars", "advisor": "Cohen, Marshall H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09252008-135215", "creators": [ { "name": { "family": "Putney", "given": "Angela" }, "id": "Putney-A", "display_name": "Putney, Angela" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Marshall H." }, "id": "Cohen-M-H", "role": "advisor", "display_name": "Cohen, Marshall H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/mq60-yx71", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nThree aspects of magnetic white dwarf stars are studied to aid in the understanding of stellar evolution.\r\n\r\nA survey of ~ 50 DC white dwarf stars was conducted in circular spectropolarimetry to search for magnetic fields [...] 30 kG. Four DC stars were discovered with magnetic fields above 30 kG: G 111-49 with B[subscript e] ~ \u2014220 MG, G 183-35 with B[subscript e] = +6.8 \u00b1 0.5 MG, G 256-7 with B[subscript e] = +4.9 \u00b1 0.5 MG, and G 234-4 with B[subscript e] = +39.6 \u00b1 11.6 kG. A new magnetic DB white dwarf was also discovered, LB 8827 with B[subscript e] = 1.0 \u00b1 0.5 MG. A total of 15% of the white dwarfs in the survey have a magnetic field > 30 kG. This value is far larger than the 2% of DA stars, but more than half of the DC stars were originally misclassified. Only 5% of the re-classified DC stars have magnetic fields above 30 kG.\r\n\r\nThree magnetic stars from the DC white dwarf survey were re-observed to investigate the possibility of rotation. Two are definitely rotating: LHS 1734 with 16 min [...] P < 1 yr and G 158-45 (=LHS 1044) with a probable period P ~ 11 hr but a definite period P [...] 1 d or P ~ a few days. G 183-35 might be rotating with 50 min [...] P < a few yr. From all the white dwarf rotations known, it is clear that angular momentum is lost before a star becomes a white dwarf, but not clear that the loss is greatly enhanced by magnetic fields.\r\n\r\nThe isolated magnetic white dwarfs G 99-47, KUV 813-14 (KUV 23162-1220), and G 227-35 were observed in linear and circular spectropolarimetry and then compared to calculated theoretical spectra to find a model for the magnetic field strength and structure. The comparisons were to Stokes' V/I (circular polarization) spectra in addition to total flux F[...], and these add many constraints to the possible solutions. An off-centered dipole or a dipole+quadrupole configuration best fits the observations.\r\n\r\nThe results of the survey and the modeling are consistent with the theory that the magnetic Ap stars are the predecessors of magnetic white dwarfs.\r\n" }, { "name": "Xu, Wenge", "degree": "PhD", "year": "1995", "title": "The first Caltech-Jodrell Bank VLBI survey", "advisor": "Readhead, Anthony C. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10262007-132906", "creators": [ { "name": { "family": "Xu", "given": "Wenge" }, "id": "Xu-Wenge", "display_name": "Xu, Wenge" } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/k8f8-gn20", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis thesis presents the author's major contributions to the first Caltech-Jodrell Bank VLBI survey (CJ1). It demonstrates convincingly that the VLBI snapshot technique is a reliable and highly efficient method of making images of large samples of objects.\r\n\r\nThe CJ1 sample consists of 135 objects with 1.3 Jy > [...] GHz [...] 0.7 Jy, [...](1950) [...] 35\u00b0 and [...] > 10\u00b0. The combination of the CJ1 sample with the Pearson-Readhead sample provides a complete, flux density limited sample of 200 objects with [...] GHZ [...] 0.7 Jy, [...](1950) [...] 35\u00b0 and [...] > 10\u00b0 for which all of the objects accessible to Mark II VLBI have been mapped at both 5 GHz and 1.6 GHz. In this thesis we present the 5 GHz VLBI observations from the CJ1 survey and follow-up observations of 8 compact symmetric objects (CSO) or CSO candidates at 8.4 GHz. In addition, we present 5 GHz MERLIN observations of 20 objects and 1.4 GHz VLA observations of 92 objects in the CJ1+PR sample. The VLA maps, together with L band (1.3-1.7 GHz) maps available in the literature, provide a complete set of VLA maps for the CJ1+PR sample. Furthermore, we present new redshifts, optical counterparts and optical polarimetry measurements of the objects in the CJ1 sample.\r\n\r\nBased on morphological attributes on scales < 5 kpc and [...] 5 kpc, we identify six physically distinct classes in the CJ1+PR sample, one of which is the CSO class. Identification of CSO's may have a profound impact on our understanding of AGN. Detailed study of one archetypal CSO, 2352+495, has demonstrated that the CSO's are likely a class of short-lived powerful galaxies.\r\n\r\nWe have confirmed the bimodal distribution of the misalignment angle and identified that the peak near 90\u00b0 is contributed by a group of objects with high optical polarization, high fractional core flux, high radio variability and flat radio spectrum. All of these are symptoms of relativistic beaming.\r\n\r\nThe mean angular sizes of the CJ1+PR objects show only slight dependence on redshift, contrary to the finding by Kellermann. However, our results show that the angular size distributions of objects with z < 0.1 and those with z > 0.1 are significantly different. This may indicate an evolutionary effect.\r\n" }, { "name": "Rand, Richard J.", "degree": "PhD", "year": "1991", "title": "The relationship between the density wave, molecular gas and star formation in M51", "advisor": "Kulkarni, Shrinivas R.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09162008-105121", "creators": [ { "name": { "family": "Rand", "given": "Richard J." }, "id": "Rand-R-J", "display_name": "Rand, Richard J." } ], "advisors": [ { "name": { "family": "Kulkarni", "given": "Shrinivas R." }, "id": "Kulkarni-S-R", "role": "advisor", "display_name": "Kulkarni, Shrinivas R." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/c2j4-qh42", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nA study is presented of the relationship between the density wave, molecular gas and star formation in the molecule-rich, grand-design spiral galaxy M51.\r\n\r\nAn interferometric map of CO emission covering most of the disk of M51 at 8\" resolution is presented. A narrow, two-arm spiral pattern is seen in the molecular gas. Streaming motions indicating the presence of a density wave can clearly be seen. Giant Molecular Associations (GMAs) of typical mass 3 x 10[superscript 7] M[...], first reported by Vogel, Kulkarni and Scoville, are seen in abundance along the arms. The virial theorem indicates that these GMAs are roughly gravitationally bound. A few unbound GMAs are also seen between the arms. There is evidence that these interarm GMAs form in a secondary compression of the density wave. Substructure in the GMAs is indicated by their CO spectra, which typically reveal a few discrete velocity components.\r\n\r\nHigher (2.5\") resolution maps of a small area south of the nucleus of M51 reveal patchy substructure along the southern molecular spiral arm and in the GMAs. The above-mentioned streaming motions are confirmed at this resolution. The one-dimensional velocity dispersion along the arms at this resolution is roughly 10 km s[superscript -1]. A more careful virial analysis confirms that the on-arm GMAs are bound while the interarm GMAs are unbound. The on-arm GMAs are shown to be stable against galactic tidal forces, while the interarm GMAs are close to the point of marginal stability. Along the spiral arm in this map, the detailed agreement between CO and H\u03b1 luminosity is poor. There are several possible explanations for this.\r\n\r\nTwo consequences of star formation on the state of the ISM of M51 are discussed. Using the new, 8\"-resolution VLA map of 21-cm emission, we find much new evidence in support of the idea of Tilanus and Allen that the HI is predominantly a product of dissociation in star-forming regions. The possibility is suggested that HI emission may be used as an indicator of star formation efficiency in molecule-rich galaxies.\r\n\r\nIRAS pointed observations of M51 are used to probe the origins of the infrared emission. Two independent tests indicate that a substantial fraction of the infrared emission originates in a cirrus component, and not due to dust heating by star-forming regions. One consequence of the existence of the cirrus component is that infrared emission cannot be used in a straightforward way to test the hypothesis of the triggering of star formation by a density wave.\r\n\r\nA kinematic study of the old-disk stars, and the molecular, neutral and ionized gas is presented. The old-disk stars, since they comprise most of the mass of the galaxy, trace the underlying gravitational perturbation. Long-slit spectroscopy of the absorption lines provides some evidence for radial streaming motions in the massive old-disk population. The amplitude of the motion at 85\" from the nucleus is greater than that expected from linear density wave theory. A possible explanation from nonlinear theory is given. Long-slit spectroscopy of the [...] and [NII] lines, along with kinematic information from our CO map and the high-resolution VLA map of 21-cm emission, clearly reveal streaming motions in the molecular, neutral and ionized gas. These motions are compared with the predictions of nonlinear density wave models.\r\n\r\nA quantitative analysis of possible GMA formation mechanisms, which draws on our morphological and kinematic observations of the molecular gas, is presented. Gravitational instability and collisional agglomeration are both viable mechanisms for GMA formation on the arms. The interarm gas is close to the point of marginal stability, and the postulated secondary compression of the density wave may be sufficient to cause either weak instabilities in the gas, or low-level orbit crowding, thereby explaining the unbound interarm GMAs. The relationship between GMA formation and the triggering of star formation is briefly addressed. Problems with the conclusion that the on-arm GMAs are gravitationally bound are discussed. Disruption of bound on-arm GMAs must be rapid since they are confined to narrow spiral arms. Although the arguments are by no means conclusive, the input power of star formation is a plausible mechanism for GMA disruption.\r\n" }, { "name": "Grossman, Arie William", "degree": "PhD", "year": "1990", "title": "Microwave imaging of Saturn's deep atmosphere and rings", "advisor": "Muhleman, Duane Owen", "url": "https://resolver.caltech.edu/CaltechETD:etd-10302008-151649", "creators": [ { "name": { "family": "Grossman", "given": "Arie William" }, "id": "Grossman-Arie-William", "display_name": "Grossman, Arie William" } ], "advisors": [ { "name": { "family": "Muhleman", "given": "Duane Owen" }, "id": "Muhleman-D-O", "role": "advisor", "display_name": "Muhleman, Duane Owen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "plansci" ], "doi": "10.7907/svtf-j306", "abstract": "This work presents an analysis of microwave images of Saturn's atmosphere and rings. Interferometer observations at wavelengths of 0.27, 2.01, 3.53, 6.17, and 20.13 centimeters and precise application of synthesis imaging techniques yielded brightness and polarization maps of unsurpassed resolution and sensitivity. Linear polarization is detected from the ring ansea, and brightness variations in the deep atmosphere and the rings are revealed for the first time.\r\n\r\nThe disk-integrated spectrum of Saturn is interpreted within the context of a radiative transfer model that requires the NH3 mixing ratio to take on a value of 0.9 to 1.1 x10[superscript -4] (0.5-0.6 times solar) directly below the ammonia ice cloud at a pressure of 1.4 bar. The NH[subscript 3] mixing ratio increases with depth to a value of 5.0 to 6.5 x10[superscript -4] (2.9-3.7 times solar) at a pressure of 6 bar. The variation of NH3 with depth can be entirely accounted for by the presence of 11-14 times solar abundance of H[subscript 2]S, which reacts with NH[subscript 3] to produce a substantial NH[subscript 4]SH cloud.\r\n\r\nLatitudinal variations in brightness temperature indicate that the saturated vapor abundance of ammonia decreases by 50% from equator to pole within the cloud deck. At greater depths the latitudinal variations of ammonia are consistent with alternating zones of concentration and depletion caused by vertical motions. An apparent depletion in northern mid-latitudes is well-correlated with a decrease in infrared opacity and depressed cloud top levels, indicating deep-seated downwelling.\r\n\r\nThe size, composition, and shape of particles comprising the rings of Saturn are constrained by modeling the emission, scattering, and extinction of radiation by the rings. The observations can be fit by a incremental power-law particle size distribution with exponent in the range 2.6-3.0 for the combined A and B rings, assuming a classical many-particle-thick layer. The wavelength dependence of the optical depths places a strict lower limit of 1 cm on particle sizes in the classical rings. Observations of thermal emission from the rings further constrain the mass fraction of uniformly mixed silicate impurities to be less than 1%. Azimuthal variations in brightness and linear polarization rule out the possibility that the particles are smooth, convex objects, and favor a model in which the particles are irregularly shaped.\r\n" }, { "name": "Myers, Steven Theodore", "degree": "PhD", "year": "1990", "title": "A Search for Anisotropy in the Cosmic Microwave Background on Angular Scales of 1 to 30 Arcminutes", "advisor": "Readhead, Anthony C. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09102008-135630", "creators": [ { "name": { "family": "Myers", "given": "Steven Theodore" }, "id": "Myers-Steven-Theodore", "display_name": "Myers, Steven Theodore" } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." } ], "committee": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "chair", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Mould", "given": "Jeremy R." }, "id": "Mould-J-R", "orcid": "0000-0003-3820-1740", "role": "member", "display_name": "Mould, Jeremy R." }, { "name": { "family": "Sargent", "given": "Wallace L. W." }, "id": "Sargent-W-L-W", "role": "member", "display_name": "Sargent, Wallace L. W." }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "orcid": "0000-0002-9656-4032", "role": "member", "display_name": "Phinney, E. Sterl" } ], "option_major": [ "astronomy" ], "doi": "10.7907/p4e7-rw11", "abstract": "Observations at a frequency of 20 GHz from the Owens Valley Radio Observatory with the 40-meter diameter radiotelescope are used to place limits on the anisotropy of the cosmic microwave background radiation, believed to be a relic from the Big Bang. Two experiments, designated NCP and RING, were performed with the former consisting of deep measurements in 8 fields at the declination \u03b4 = 89\u00b0 and the latter a survey of 96 fields at declination \u03b4 = 88\u00b0 10'42\". Bayesian statistical analysis of the 8 NCP field observations place a 95% confidence upper limit of \u03b4T/T < 1.9 x 10-5 (in fractions of the microwave background temperature 2.735 K) and 4.2 x 10-5 for 99.87% confidence (3\u03c3) on the amplitude of fluctuations with a characteristic correlation length of 2'.6. The 96 fields of the RING experiment were observed in an interlocked ring-like geometry to enhance the sensitivity of the experiment to larger-scale anisotropies. Because of the larger area of sky covered, this data was more susceptible to contamination by discrete extragalactic radio sources and separate lower frequency observations were used to identify and correct for the contributions of these objects. The statistical analysis of the RING data results in the limits on the anisotropy of 2.5 < \u03b4T/T < 5.0 x 10-5 (95%) and 1.9 < \u03b4T/T < 6.1 x 10-5 (99.87%) for fluctuations with a correlation angle of 2'.6. Because of the high probability of residual discrete source contamination, these results are treated as upper limits on intrinsic background fluctuations. These experiments constrain the amplitude to be less than 3 x 10-4 for correlation angles between 0'.1 and 30' (95%). The implications for cosmology and theories of galaxy formation are discussed, and models without significant non-baryonic matter and/or non-standard recombination are excluded by the observations.\r\n" }, { "name": "Wilson, Christine Diana", "degree": "PhD", "year": "1990", "title": "Star formation and the interstellar medium in M33", "advisor": "Scoville, Nicholas Zabriskie", "url": "https://resolver.caltech.edu/CaltechETD:etd-09152008-110204", "creators": [ { "name": { "family": "Wilson", "given": "Christine Diana" }, "id": "Wilson-C-D", "display_name": "Wilson, Christine Diana" } ], "advisors": [ { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "role": "advisor", "display_name": "Scoville, Nicholas Zabriskie" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/sqk4-dx41", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nNew millimeter-wave and optical data are used to study high-mass star formation and its relationship with the interstellar medium in the inner 4' radius of the nearby spiral galaxy M33. The total mass of molecular hydrogen in this region is 3.4x10[superscript 7] M[...], roughly twice the mass in atomic hydrogen. The predicted atomic hydrogen column density from atomic mantles of molecular clouds is similar to the observed mean atomic hydrogen column density. Thus probably only a small fraction of the atomic hydrogen is in a diffuse component not directly associated with molecular clouds.\r\n\r\nThe properties of 38 individual molecular clouds in M33 (velocity widths, diameters, peak brightness temperatures, and masses) are very similar to those of Galactic molecular clouds. Masses derived from the virial theorem and from the integrated CO fluxes agree to within 10%, which implies that the value of the conversion factor from CO flux to H[subscript 2] column density, \u03b1, is the same in M33 and the Galaxy. This is the first direct measurement of the value of \u03b1 in an external galaxy.\r\n\r\nThe mass distribution of clouds in M33 is consistent with that derived in the Galaxy for M = 0.8 - 4 x 10[superscript 5] M[...], but shows a total lack of clouds with masses greater than 4 x 10[superscript 5] M[...]. A simple model is proposed to explain the high-mass cutoff to the mass distribution as arising from the competing processes of cloud growth through accretion and cloud destruction due to star formation. Comparison of the flux detected with the interferometer with single dish data indicates that 50% of the molecular gas resides in structures less massive than 0.8 x10[superscript 5] M[...], in contrast to the Galaxy where only 15% of the molecular gas mass is in these smaller structures.\r\n\r\n41 OB associations each containing at least ten blue stars have been identified in this region of M33. The associations have mean radii of 40 pc, masses in stars of mass > 20 M[...] of 600 M[...], and ages of 8x10[superscript 6] yr. No evidence is found for a gradient in the ratio of blue to red supergiants in the inner two kiloparsecs of M33, despite a factor of two decrease in the metallicity over this range of radius. The blue luminosity function for stars in the field is deficient at bright magnitudes relative to the luminosity function for stars in associations. In addition, the associations in the northern arm contain no stars more massive than 20 M[...] while associations in the southern arm contain several stars with masses of 60 M[...]. These differences may be due to a sudden cessation of star formation resulting in a larger mean age for the stars or to a smaller upper mass cutoff to the initial mass function in the field and the northern arm.\r\n\r\nThe offset between the molecular and atomic gas peaks in the southern spiral arm is consistent with streaming motions expected as the gas enters a spiral density wave. In addition, the OB associations in the southern spiral arm show a weak age gradient perpendicular to the arm, consistent with the presence of a density wave. However, the northern arm has an age gradient running along the arm, as would be expected for a stochastic star formation arm.\r\n\r\nA comparison of the spatial distributions of the H\u03b1, CO, and HI emission peaks indicates that the atomic gas is probably formed via photo-dissociation of the molecular gas by recent high-mass star formation. Roughly two-thirds of the molecular clouds with M > 0.5 x 10[superscript 5] M[...] contain recent massive star formation with inferred high-mass star formation rates for individual clouds ranging from 5x10[superscript -6] to 5x10[superscript -4] M[...] yr[superscript -1]. The photo-dissociating flux produced by these stars is sufficient to produce the amount of atomic gas near the molecular clouds if the molecular clouds have a clumped structure.\r\n\r\nThe high-mass star formation rate and efficiency are measured by combining optical, far-infrared, and millimeter data. The high-mass star formation rate calculated from the H\u03b1 emission is 0.007 M[...] yr[superscript -1] over an area of 5 kpc[superscript 2], which corresponds to a total star formation rate of 0.04 M[...] yr[superscript -1]. The star formation rate obtained from the far-infrared emission agrees with the rate obtained from the H\u03b1 emission to within a factor of two. A lower limit to the high-mass star formation rate obtained from number counts of blue stars is consistent with the rates obtained from H\u03b1 and far-infrared emission. The southern spiral arm and the molecular complexes have similar star formation efficiencies to regions of the galaxy containing little molecular gas. Thus the large amount of star formation occurring in the spiral arms of M33 is due to the presence of large amounts of molecular gas and not to an increased star formation efficiency.\r\n" }, { "name": "Barsony, Mary Anne", "degree": "PhD", "year": "1989", "title": "Outflows in High Mass Star-Forming Regions", "advisor": "Scoville, Nicholas Zabriskie", "url": "https://resolver.caltech.edu/CaltechETD:etd-09102008-084535", "creators": [ { "name": { "family": "Barsony", "given": "Mary Anne" }, "id": "Barsony-Mary-Anne", "display_name": "Barsony, Mary Anne" } ], "advisors": [ { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "role": "advisor", "display_name": "Scoville, Nicholas Zabriskie" } ], "committee": [ { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "role": "chair", "display_name": "Scoville, Nicholas Zabriskie" }, { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "role": "member", "display_name": "Blake, Geoffrey A." }, { "name": { "family": "Goldreich", "given": "Peter Martin" }, "id": "Goldreich-P-M", "role": "member", "display_name": "Goldreich, Peter Martin" }, { "name": { "family": "Libbrecht", "given": "Kenneth George" }, "id": "Libbrecht-K-G", "role": "member", "display_name": "Libbrecht, Kenneth George" } ], "option_major": [ "physics" ], "doi": "10.7907/FDFC-0Q12", "abstract": "In the last decade, observations of star-forming regions in the millimeter wavelength range have led to the discovery of supersonic molecular outflows from embedded infrared sources, a heretofore unsuspected, but now generally accepted, phase in the star formation process. In order to better understand the outflow phenomenon in high mass (i.e., high luminosity) pre-main sequence stars, the three sources S87, LkH\u03b1101, and S106 were chosen for closer study. Observations from the recently completed Owens Valley Radio Observatory's millimeter wave interferometer afford us the highest spatial-resolution, molecular line (CS J=2\u21921 and 13CO J=1\u21920) maps of these sources to date. The OVRO maps were combined with data from the 14 m FCRAO millimeter wave radio telescope, the VLA, IRAS, and the Palomar 5 m and 1.5 m optical telescopes.
\r\n\r\nA synthesis of the data reveals that although all three pre-main sequence objects are the sources of powerful, ionized stellar winds, only one, S87/IRS1, currently drives a bipolar molecular outflow. The inferred mass loss rates in the winds of S87/IRS1, LkH\u03b1101, and S106 IR are 1.8 x 10-5, 1.7 x 10-6, 1.1 x 10-5 M\u2609 yr-1, with corresponding wind velocities of 160, 350, and 200 km s-1. In all cases the wind velocities are lower, and the mass loss rates higher, than for main sequence stars of the same spectral types. Radiation pressure is inadequate to drive these winds, which can be anisotropic in their velocity fields.
\r\n\r\nThe existence of massive, large-scale (r \u2248 1016 cm) disks, necessary for numerous proposed molecular outflow models, can now be ruled out. Only one of the many proposed molecular outflow models is consistent with the new observations (K\u00f6nigl 1982).
\r\n\r\nAlthough the observed winds can disperse a good portion of the cloud cores they inhabit, they cannot completely destroy these cores. Consequently, outflows from pre-main sequence stars alone cannot account for the dispersal of molecular clouds, as some investigators have suggested.
\r\n\r\nTwo glaring and intriguing problems remain to be solved in this field: the origin of the supersonic turbulence observed throughout a molecular cloud, and the driving mechanism of the powerful, ionized winds found in the high-mass, pre-main sequence stars.
\r\n" }, { "name": "Cheung, Kwok-wai", "degree": "PhD", "year": "1987", "title": "An Acousto-Optical Correlation Spectrometer for Radio Astronomy", "advisor": "Moffet, Alan Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-08282008-094735", "creators": [ { "name": { "family": "Cheung", "given": "Kwok-wai" }, "id": "Cheung-Kwok-wai", "display_name": "Cheung, Kwok-wai" } ], "advisors": [ { "name": { "family": "Moffet", "given": "Alan Theodore" }, "id": "Moffet-A-T", "role": "advisor", "display_name": "Moffet, Alan Theodore" } ], "committee": [ { "name": { "family": "Moffet", "given": "Alan Theodore" }, "id": "Moffet-A-T", "role": "chair", "display_name": "Moffet, Alan Theodore" }, { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "member", "display_name": "Phillips, Thomas G." }, { "name": { "family": "Scoville", "given": "Nicholas Zabriskie" }, "id": "Scoville-N-Z", "role": "member", "display_name": "Scoville, Nicholas Zabriskie" }, { "name": { "family": "Drever", "given": "Ronald W. P." }, "id": "Drever-R-W-P", "role": "member", "display_name": "Drever, Ronald W. P." } ], "option_major": [ "physics" ], "doi": "10.7907/pvms-m577", "abstract": "The objective of this thesis research is to develop and construct a wide-band, high resolution, two-channel prototype acousto-optic correlation spectrometer (AOCS) to analyze signals received by the three element millimeter-wave interferometer at Caltech's Owens Valley Radio Observatory (OVRO) which may be used to study the distribution of carbon monoxide and other molecules in galaxies.
\r\n\r\nThe proposed correlation spectrometer has the main advantage of large time-bandwidth products and hence of low cost per frequency channel. Thus, it is suitable for many scientific objectives that require both large bandwidth and high resolution, such as mapping the distribution and temperature of the interstellar gases of galactic sources and extragalactic sources or studying the atmospheric conditions of planets in the solar system.
\r\n\r\nPhase switching has been used to reduce the zero level variation of this instrument, and is found to be more effective than other schemes used by the single dish acousto-optical spectrometers.
\r\n\r\nBoth the frequency resolution and the frequency coverage of this instrument can be changed easily, and give it a flexibility not attainable by the filter-bank spectrometers. The relative light weight and compactness of this instrument make it a good candidate for outer space applications.
\r\n\r\nAn absolute calibration of the instrument has been attempted by using the system temperature as a scale for both the correlated signal received and the noise fluctuation of the instrument. A statistical method has been used to measure the various noise contributions of the instrument, which allows a very precise characterization of the zero level stability and the noise degradation of the system. The visibility loss of the present instrument was measured to be about 50%, and the noise degradation was about 40%. These losses were not due to any theoretical limitations but were the results of the imperfections in the present setup. They can be improved in the future versions of this instrument.
\r\n\r\nThis instrument can be used to measure any RF spectrum and the cross spectrum of any two RF signals. Since it is a time integrating device, its sensitivity can be as high as one desires. With phase switching, one can compare the frequency characteristics of two closely matched microwave devices with great sensitivity. Because of its compactness, low cost and high sensitivity, it could be a useful and practical instrument for microwave measurements.
" }, { "name": "Lind, Kevin Robert", "degree": "PhD", "year": "1987", "title": "Observations and Gas Dynamics of Extragalactic Radio Jets", "advisor": "Blandford, Roger D.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-091639", "creators": [ { "name": { "family": "Lind", "given": "Kevin Robert" }, "id": "Lind-Kevin-Robert", "display_name": "Lind, Kevin Robert" } ], "advisors": [ { "name": { "family": "Blandford", "given": "Roger D." }, "id": "Blandford-R-D", "role": "advisor", "display_name": "Blandford, Roger D." } ], "committee": [ { "name": { "family": "Blandford", "given": "Roger D." }, "id": "Blandford-R-D", "role": "chair", "display_name": "Blandford, Roger D." }, { "name": { "family": "Cohen", "given": "Donald S." }, "id": "Cohen-D-S", "role": "member", "display_name": "Cohen, Donald S." }, { "name": { "family": "Phinney", "given": "E. Sterl" }, "id": "Phinney-E-S", "role": "member", "display_name": "Phinney, E. Sterl" }, { "name": { "family": "Sturtevant", "given": "Bradford" }, "id": "Sturtevant-B", "role": "member", "display_name": "Sturtevant, Bradford" } ], "option_major": [ "astronomy" ], "doi": "10.7907/wnqa-gn45", "abstract": "This thesis is a combined observational and theoretical study of extragalactic radio jets. Jets are defined observationally as extended, center-brightened features, which are observed in radio images at all resolution scales. They are defined theoretically as momentum-dominated, well-collimated plasma flows. There is now little debate as to the basic interpretation of radio jets as actual plasma outflows, but the detailed dynamics of the jets, or even whether the kiloparsec-scale jets are relativistic, are still uncertain. The resolution of the details of the physics of jets requires improved radio images, especially at the base of the jet, and detailed models of jets. Maps of the base of the radio jet can only be obtained with VLBI observations; detailed jet models require numerical simulations on a supercomputer.
\r\n\r\nThe observational work was a large global VLBI observation of the N galaxy 3C371. The goal was to detect and, if possible, map the underlying jet. This was done, and the results compared with a previous VLBI map, and with maps from other interferometers at lower resolution. No conclusions could be drawn regarding the nature of the jet, although it was clear that the jet was active, and appeared to vary on short time scales.
\r\n\r\nThe theoretical work was in two parts, both of which were directed toward refining existing theories. The first part was to calculate the emission for relativistically moving patterns which themselves contain relativistic flows, to determine how much the flux as a function of viewing angle may vary between realistic models of the knots in relativistic jets. It was found that considerable variation was possible, and that superluminal expansion rates were not necessarily good determiners of the bulk flow rate. The second part was to develop a code to simulate axisymmetric magnetized jets propagating into a uniform medium. This was implemented for the case of toroidal field only, and run for a moderately magnetized injected jet. It was found that, although most of the jet dynamics was determined by the nonmagnetic forces, the influence of the magnetic tension focused the flow sufficiently to significantly increase the speed of advance of the jet.
\r\n" }, { "name": "Biretta, John Anthony", "degree": "PhD", "year": "1986", "title": "Investigations of Radio Jets in M87, 3C273, and 3C345", "advisor": "Cohen, Marshall H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-084712", "creators": [ { "name": { "family": "Biretta", "given": "John Anthony" }, "id": "Biretta-John-Anthony", "display_name": "Biretta, John Anthony" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Marshall H." }, "id": "Cohen-M-H", "role": "advisor", "display_name": "Cohen, Marshall H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/dsst-qp22", "abstract": "We present observational studies of extra-galactic radio jets in M87, 3C273, and 3C345.
\r\n\r\nObservations of the M87 jet were made at 15 GHz with 0.12\" resolution. All of the knots are clearly resolved both along and across the jet. Most of the knots are found to be smooth in appearance with no evidence of shocklike discontinuities. The brightest knot and the innermost knot are exceptions to this. The brightest knot (knot A) seems consistent with a shock caused by unsteady flow in the jet. Models for this feature are discussed. Combining our data with X-ray data suggests that the jet is neither freely expanding, thermally confined, nor ram pressure confined. The jet may, however, be magnetically confined.
\r\n\r\nWe present 10.7 GHz VLBI observations of 3C273 with high north-south resolution. A strong, non-monotonic curvature is found in the jet at projected radii \u2264 5 pc. It is unlikely that this curvature can be caused by precession. Measurements of the core size show that bulk relativistic motion in the core is not required for consistency with the observed x-ray flux.
\r\n\r\nFor 3C345 we present a systematic analysis of VLBI observations at 2.3, 5.0, 10.7, 22.2, and 89 GHz. Epochs are from 1979.25 through 1984.11. A newly ejected superluminal component (C4) is observed to accelerate, change position angle, undergo a large flux outburst, and have a flat spectrum. Older components C2 and C3 have different speeds, different position angles, and show little or no acceleration. The spectrum of C3 steepens as its flux decays. There are spectral index gradients such that both C4 and C3 are farther from the \"core\" at higher frequencies. The moving components define an opening angle of ~27\u00b0 and also show direct evidence for expansion. The counter-jet to jet flux ratio is extremely small, -0.007\u00b10.007.
\r\n\r\nThese data for 3C345 are interpreted in terms of simple models involving spherical components or shocks in a relativistic jet. All of the emission regions show evidence for bulk relativistic motion with \u03b4 > 3. The particle energies and pressures dominate those of the magnetic fields, unless \u03b4 \u2265 20. If the emission regions consist of an electron-proton plasma, then the density of thermal electrons is much less than the density of relativistic electrons. The fluxes decay with time much more rapidly than the synchrotron half-life, but much more slowly than predicted by adiabatic expansion. An attractive model for the observed kinematics identifies the emitting regions as shocks in an apparently broad and curved jet; a curvature of \u2265 3\u00b0 and \u03b3 \u2265 10 is required.
\r\n" }, { "name": "Hough, David Hans", "degree": "PhD", "year": "1986", "title": "Parsec-Scale Structure in the Nuclei of Double-Lobed Radio Quasars", "advisor": "Readhead, Anthony C. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09102008-091002", "creators": [ { "name": { "family": "Hough", "given": "David Hans" }, "id": "Hough-David-Hans", "display_name": "Hough, David Hans" } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." } ], "committee": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "chair", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Cohen", "given": "Marshall H." }, "id": "Cohen-M-H", "role": "member", "display_name": "Cohen, Marshall H." }, { "name": { "family": "Blandford", "given": "Roger D." }, "id": "Blandford-R-D", "role": "member", "display_name": "Blandford, Roger D." }, { "name": { "family": "Schmidt", "given": "Maarten" }, "id": "Schmidt-M", "role": "member", "display_name": "Schmidt, Maarten" } ], "option_major": [ "astronomy" ], "doi": "10.7907/8P47-SM58", "abstract": "A complete sample of double-lobed quasars is defined, which is believed to be randomly oriented and which contains many objects with central components accessible to very-long-baseline interferometry (VLSI). The purpose of defining the sample in this way is to facilitate tests of physical models proposed to explain both the compact and extended structures in extragalactic radio sources. Statistical studies of the properties of these objects on the >~ kiloparsec scale are consistent with the assumption of random orientations and the simple relativistic beaming theory.
\r\n\r\nThe central components of six double-lobed quasars have been mapped at high resolution and high sensitivity with VLBI. Each object exhibits a double or extended structure on the the ~parsec scale. This structure can be interpreted as a \"core-jet,\" the same morphology found in the dominant cores of powerful flat-spectrum sources, thus indicating a relation between the two classes of compact radio source. The presumed VLBI jets are all fairly well aligned with >~kiloparsec-scale, one-sided jets. The fact that the VLBI and large-scale jets always lie on the same side of the compact core suggests the same cause for the asymmetric structure on both scales.
\r\n\r\nThe central components of 3C245 and 3C263 have been mapped at three epochs. We find superluminal expansion in 3C263 with an apparent velocity of ~1.5c, and argue that there is evidence that 3C245 will also be found to be superluminal. These results are consistent with the simple beaming theory. It is thus clear that we will be able to measure component motion in many of these objects, which will permit us to distinguish among alternative theories of parsec-scale structure and motion.
\r\n\r\nThe future study of these compact central components will benefit greatly from the increased resolution afforded by both higher frequency, ground-based VLBI and VLBI using a radio telescope in Earth orbit.
\r\n" }, { "name": "Lichten, Stephen Morris", "degree": "PhD", "year": "1984", "title": "Turbulence and Mass Motion in Galactic Molecular Clouds", "advisor": "Wannier, Peter G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-083043", "creators": [ { "name": { "family": "Lichten", "given": "Stephen Morris" }, "id": "Lichten-Stephen-Morris", "display_name": "Lichten, Stephen Morris" } ], "advisors": [ { "name": { "family": "Wannier", "given": "Peter G." }, "id": "Wannier-P-G", "role": "advisor", "display_name": "Wannier, Peter G." } ], "committee": [ { "name": { "family": "Phillips", "given": "Thomas G." }, "id": "Phillips-T-G", "role": "chair", "display_name": "Phillips, Thomas G." }, { "name": { "family": "Oke", "given": "J. Beverly" }, "id": "Oke-J-B", "role": "member", "display_name": "Oke, J. Beverly" }, { "name": { "family": "Goldreich", "given": "Peter Martin" }, "id": "Goldreich-P-M", "role": "member", "display_name": "Goldreich, Peter Martin" }, { "name": { "family": "Wannier", "given": "Peter G." }, "id": "Wannier-P-G", "role": "member", "display_name": "Wannier, Peter G." } ], "option_major": [ "astronomy" ], "doi": "10.7907/wbm2-9x67", "abstract": "The main subject of this thesis is the origin and maintenance of supersonic gas motions in dense molecular clouds.
\r\n\r\nIn Chapters 1 and 2, we interpret and model millimeter wavelength CO line profiles whose broad wings and self-reversals provide clues about the nature of the observed supersonic motions. Broad molecular line wings provide evidence for high-velocity bipolar gas flows powered by strong stellar winds. The self-reversed CO line profiles are due in part to radiative transfer effects in molecular clouds which, in some cases, are expanding or contracting; Monte Carlo simulations of radiative transfer, however, demonstrate that cloud fragmentation may be responsible for some observed properties of the line profiles. The detection of broad-wing sources in quiescent, dark nebulae, shows that energetic outflows are common in a wide range of molecular clouds.
\r\n\r\nIn Chapter 3, our high resolution maps of molecular and atomic line emission across molecular cloud edges show that these clouds are embedded in warm H I halos which appear in emission against the galactic H I background. We also find that molecular cloud internal motions may be correlated with the H I halo temperature; however, the halo masses are much less than those of the molecular clouds and exert only a limited influence on internal cloud kinematics.
\r\n\r\nThe statistical and autocorrelation analyses of Chapters 4 and 5 show that molecular clouds are clumpy and contain hundreds of turbulent fragments whose relative velocities are supersonic, but whose internal velocity dispersions are not. Shock dissipation processes, clump collisions, and gas compression have major roles in molecular cloud kinematics. Our observations indicate that turbulent energy is supplied at small scales, as opposed to the dissipationless energy transfer from large to small scales which is known to occur in incompressible fluids with high Reynolds numbers. Energetic outflows from embedded young stars may break apart, fragment, and compress portions of molecular clouds, and may be capable of originating and sustaining the supersonic turbulence. Additional observational and theoretical studies of cloud clumpiness and of the rate of energy transfer from stellar outflows to ambient molecular material, are required before this mechanism for cloud support can be evaluated.
\r\n" }, { "name": "Simon, Richard Stanley", "degree": "PhD", "year": "1983", "title": "Nuclear Structure of Quasars at 329 Megahertz", "advisor": "Readhead, Anthony C. S.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-093723", "creators": [ { "name": { "family": "Simon", "given": "Richard Stanley" }, "id": "Simon-Richard-Stanley", "display_name": "Simon, Richard Stanley" } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." } ], "committee": [ { "name": { "family": "Blandford", "given": "Roger D." }, "id": "Blandford-R-D", "role": "chair", "display_name": "Blandford, Roger D." }, { "name": { "family": "Cohen", "given": "Marshall H." }, "id": "Cohen-M-H", "role": "member", "display_name": "Cohen, Marshall H." }, { "name": { "family": "Schmidt", "given": "Maarten" }, "id": "Schmidt-M", "role": "member", "display_name": "Schmidt, Maarten" }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." } ], "option_major": [ "astronomy" ], "doi": "10.7907/zyfw-8c64", "abstract": "In the four chapters in this thesis are presented studies of compact quasars using Very Long Baseline Interferometry at 329 MHz.
\r\n\r\nThe first chapter presents hybrid maps of two quasars, 3C147 and 3C286, made at 329 MHz from VLBI observations taken in 1975 with a three station interferometer. The observations presented in the first chapter were used to make the first detailed maps of compact radio structure at this frequency. Both objects consist of an unresolved core; an extended, asymmetric jet; and an even larger, completely resolved halo. For 3C147 it is possible to decompose the spectrum into individual component spectra; at 329 MHz the core of 3C147 is found to be strongly self-absorbed. For both sources the spectral index decreases monotonically from core to jet to halo.
\r\n\r\nThe second chapter presents further observations of quasars at 329 MHz. These observations were taken with a seven-station interferometer and were used to produce high dynamic range maps of the quasars 3C48, 3C147, 3C309.1, 3C380, and 3C454.3. These maps, made with the most extensive low-frequency VLBI observations to date, are the first reliable, high dynamic range maps at this frequency, and reveal extremely complex source structure in four of these sources. All five of the objects are seen to have asymmetric structure that can be interpreted in the \"core-jet\" picture of compact extragalactic radio sources. The jets observed in these objects are not straight, but bent; three of these quasars have bends in their structure greater than 90\u00b0 on scales of 1 - 10 kpc.
\r\n\r\nChapter three deals with the analysis of the two maps of 3C147 presented in chapters 1 and 2. Comparison of those maps reveals that the core of 3C147 is a low-frequency variable radio source which has brightened by a factor of two in six years. In combination with X-ray observations this is used to demonstrate that bulk relativistic motion is taking place within the core and leads to the prediction that 3C147 is a member of the class of \"superluminal\" radio sources. It is also found that the inclination to the line of sight of the underlying bulk relativistic motion is less than 10\u00b0.
\r\n\r\nA self-consistent picture of 3C147 as a low-frequency variable is thus developed which is consistent with the available observations, yet does not require an extreme value of the total energy: the total energy of the core of 3C147 is found to be ~1054 ergs. Together with NRAO 140 there are now two extragalactic low-frequency variable radio sources in which bulk relativistic motion has been demonstrated. Thus it may well be that bulk relativistic motion is responsible for the required time-scales in most, if not all, low-frequency variables.
\r\n\r\nIn chapter four, the observations presented in chapter two of 3C48, 3C147, 3C309.1, 3C380 and 3C4S4.3 are analyzed using standard synchrotron emission theory in order to discover the physical conditions occurring in these objects. For 3C48, the suggestion in chapter 2 of this source as a \"core-jet\" source is seen to be reasonable with fields energy density and pressure all decreasing with increasing distance from the supposed core. For 3C48, the suggestion in chapter 2 of this source as a \"core-jet\" source is seen to be reasonable, with fields, energy density, and pressure all decreasing with increasing distance from the supposed core. The pressure in the jet in 3C48 is extremely large, implying that the jet cannot be confined by external gas pressure, unless the surrounding medium has extreme values of the temperature and density. In the case of 3C147 (which was analyzed extensively in chapter 3), the halfwidth of the observed jet implies that collimation of the jet is occurring; the jet in 3C147 is definitely not a \"free\" jet. For 3C309.1, the 329 MHz observations give an upper limit to the turnover frequency for synchrotron self-absorption significantly lower than that available up to now; this limit, in combination with Einstein X-ray observations of 3C309.1, implies that bulk relativistic motion is occurring within the core of 3C309.1. Thus, the core of 3C309.1 may be very similar to the core of 3C147, and is a candidate for being both a superluminal source and a low-frequency variable. For 3C380 and 3C454.3, the limited spectral information available allows broad limits to be put on their properties.
\r\n" }, { "name": "Linfield, Roger Paul", "degree": "PhD", "year": "1981", "title": "Studies of Compact Extragalactic Radio Sources", "advisor": "Readhead, Anthony C. S.; Hall, Marshall", "url": "https://resolver.caltech.edu/CaltechETD:etd-09022008-153247", "creators": [ { "name": { "family": "Linfield", "given": "Roger Paul" }, "id": "Linfield-Roger-Paul", "display_name": "Linfield, Roger Paul" } ], "advisors": [ { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "advisor", "display_name": "Readhead, Anthony C. S." }, { "name": { "family": "Hall", "given": "Marshall" }, "id": "Hall-M", "role": "advisor", "display_name": "Hall, Marshall" } ], "committee": [ { "name": { "family": "Blandford", "given": "Roger D." }, "id": "Blandford-R-D", "role": "chair", "display_name": "Blandford, Roger D." }, { "name": { "family": "Kellerman", "given": "Kenneth I." }, "id": "Kellerman-Kenneth-I", "role": "member", "display_name": "Kellerman, Kenneth I." }, { "name": { "family": "Young", "given": "Peter J." }, "id": "Young-Peter-J", "role": "member", "display_name": "Young, Peter J." }, { "name": { "family": "Readhead", "given": "Anthony C. S." }, "id": "Readhead-A-C-S", "orcid": "0000-0001-9152-961X", "role": "member", "display_name": "Readhead, Anthony C. S." } ], "option_major": [ "astronomy" ], "doi": "10.7907/5cg5-0d24", "abstract": "Three studies of compact, extragalactic radio sources are presented.
\r\n\r\nIn the first, VLBI maps are presented of the nuclear cores of four radio galaxies which have large symmetric radio lobes: 3C 111, 3C 390.3, Cyg A, and 0055+30. Each source contains a nuclear jet having a scale of 1 pc, but no counterjets are seen. The jets in 3C 111 and 0055+30 point directly at the outer radio lobes, but in 3C 390.3 and Cyg A the jets are pointed from 4 to 6 degrees away from the lobes.
\r\n\r\nThe implications of the maps and models of these sources are considered in the second study. It is concluded that in all four cases, the observed asymmetry reflects an intrinsic asymmetry on a msec scale. The minimum pressure in the four jets is calculated, and it is concluded that the jet in Cyg A is very unlikely to be confined by gas pressure.
\r\n\r\nIn the third study, an attempt is made to explain the structure of compact radio sources with a precession-like motion or a relativistic jet. It is found that the curvature of these sources can be readily explained in this way. In addition, the knots which are often revealed by VLBI observations arise naturally in such a model. The main problem with the model is that it cannot by itself explain the arcsecond structure of asymmetric radio sources.
" }, { "name": "Romney, Jonathan Daniel MacLeish", "degree": "PhD", "year": "1979", "title": "Fine-Scale Structure of the Neutral Hydrogen Absorption in NGC1275", "advisor": "Cohen, Marshall H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09052008-131956", "creators": [ { "name": { "family": "Romney", "given": "Jonathan Daniel MacLeish" }, "id": "Romney-Jonathan-Daniel-MacLeish", "display_name": "Romney, Jonathan Daniel MacLeish" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Marshall H." }, "id": "Cohen-M-H", "role": "advisor", "display_name": "Cohen, Marshall H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/ytaj-x179", "abstract": "The high-velocity 21-cm absorption feature in NGC1275 (=3C84) has been mapped at an angular resolution of a few milliarcseconds with an intercontinental very-long-baseline interferometer. The method of analysis makes use of both the absolute amplitude of the visibility function in the continuum, and the relative amplitude and phase between the line and continuum.\r\n\r\nFine-scale structure in the continuum is determined from the observations, and the 21-cm structure of 3C84 on angular scales covering almost six orders of magnitude is reviewed.\r\n\r\nThe HI absorption is found to arise in a cloud covering part of the intense, compact continuum nucleus. Although absorption is seen against the brightest part of the continuum structure, the cloud is displaced to the northeast from the nucleus, reaching optical depths of at least 0.83. The cloud is at least 5.6 pc in diameter, with a deduced volume density between 12 and 120 cm[superscript -3].\r\n\r\nTwo basic hypotheses which have been advanced to elucidate the 21-cm absorption and other high-velocity features in NGC1275 are discussed. The results of the present investigation strongly support the interpretation that all the high-velocity features arise in a superposed galaxy in the Perseus Cluster. The alternative model, in which the high-velocity gas is ejected from the active nucleus, is inconsistent with the structure observed in the HI absorption.\r\n" }, { "name": "Schloerb, Frederic Peter", "degree": "PhD", "year": "1978", "title": "Radio Interferometric Investigations of Saturn's Rings at 3.71- and 1.30-cm Wavelengths", "advisor": "Muhleman, Duane Owen", "url": "https://resolver.caltech.edu/CaltechETD:etd-10292008-160948", "creators": [ { "name": { "family": "Schloerb", "given": "Frederic Peter" }, "id": "Schloerb-Frederic-Peter", "display_name": "Schloerb, Frederic Peter" } ], "advisors": [ { "name": { "family": "Muhleman", "given": "Duane Owen" }, "id": "Muhleman-D-O", "role": "advisor", "display_name": "Muhleman, Duane Owen" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "plansci" ], "doi": "10.7907/ztk7-wf79", "abstract": "NOTE: See Abstract within Thesis for Tables of Summary Results.\r\n\r\nInterferometric observations of Saturn and the rings have been obtained at 3.71 and 1.30 cm wavelengths. The observations have been analyzed by both model fitting and aperture synthesis techniques. They show that the rings have a very low brightness temperature, but attenuate the thermal emission from the planet significantly where they cross in front of it. The latter effect, when combined with the estimate of the ring brightness temperature, permits the optical depths of the rings to be estimated. The fits of the interferometric data to Saturn models in which the A and B rings are combined into a single ring are given in Table (1). The 3.71 cm observations were made at two epochs and the relative areas of the A and B rings that obscured the planet were different. The apparently inconsistent optical depth results of the two 3.71 cm data sets, then, indicate that the A ring optical depth is significantly less than that of the B ring. The relative areas of the A and B rings are the same for the 1976 1.30 cm and 3.71 cm observations and their optical depth results may be directly compared. They indicate that the ring optical depths are the same at the two wavelengths. These optical depths are quite similar to those estimated at visible wavelengths. The ring brightness temperatures, which are shown in the table normalized by the brightness temperature of the planet to remove any errors in the absolute calibration of the data, are also the same at the two wavelengths. No variation in the brightness temperature of the rings with tilt angle (B) was detected. A significant amount of radiation from the C ring was detected by the 3.71 cm observations, and the ring was also found to attenuate the planetary emission significantly. Unfortunately, the 1.30 cm observations were not sensitive enough to detect the C ring. The brightness temperature and optical depth results for the individual rings that are implied by all of the 3.71 cm observations are given in Table (ii). Limb-darkening of the planetary emission was simulated by solving for the best fitting planetary radius. No limb-darkening was detected at 3.71 cm, but an apparently significant amount was detected at 1.30 cm. The results at the two wavelengths are significantly different and indicate that the planet is more limb-dark at 1.30 cm than at 3.71 cm. This finding is interesting since it is contrary to what was predicted by atmospheric models which fit the Saturn microwave spectrum. The aperture synthesis analysis is independent of the model fitting and can be used to confirm its results and search for new features not included in the models. The aperture synthesis maps confirm the model fitting results and require no new brightness structures. In particular, no azimuthal variations of the brightness temperature of the rings were detected. The aperture synthesis maps also indicated that the true position of Saturn may be offset from the values given in the American Ephemeris and Nautical Almanac by about 0.3 arcsec. Consideration of simple physical models of the rings has shown that the radiation from the rings at centimeter wavelengths is almost entirely thermal emission from the planet that is scattered to the Earth by the ring particles. The models indicate that the ring particles are very good scatterers and very poor emitters at microwave wavelengths, and this conclusion sets constraints upon the size and composition of the ring particles. The similarity between the optical depths of the rings at visible and centimeter wavelengths probably indicates that the particles are much larger (\u2265 1 meter) than the centimeter wavelengths. The large sizes and excellent scattering properties of the particles indicate that they are composed of either a highly reflective or transparent material. At this time water ice is the most likely candidate, since it has been detected in the rings spectroscopically and is known to be highly transparent to microwaves at the low temperatures found at Saturn's rings.
" }, { "name": "Pigg, Jay Cee", "degree": "PhD", "year": "1976", "title": "A Limit on the Inhomogeneity of the Cosmic Microwave Background Radiation at an Angular Scale of 1.25 Arcmin", "advisor": "Moffet, Alan Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-08212008-135114", "creators": [ { "name": { "family": "Pigg", "given": "Jay Cee" }, "id": "Pigg-Jay-Cee", "display_name": "Pigg, Jay Cee" } ], "advisors": [ { "name": { "family": "Moffet", "given": "Alan Theodore" }, "id": "Moffet-A-T", "role": "advisor", "display_name": "Moffet, Alan Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/RJMF-HZ44", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn observational upper limit to the inhomogeneity of the cosmic background radiation of [...]T/T [...] 7.4 x 10[...] on an angular scale of 1.25 arcmin was obtained at a wavelength of 2.0 cm. This and Pariiskii's (1973, Astron. Zh., 50, 453 [Sov. Astron., 17, 291]) limit of [...]T/T [...] 4.8 x 10[...] at 22 arcmin define the observational upper limit to [...]T/T for all scales 1\u00b0 or less. Constraints are placed on published models of galaxy formation and 1000-Mpc scale clustering. Hypotheses that fluctuations in the background radiation could be caused by random fluctuations in the number of protogalaxies in a given solid angle, and that reionization of the intergalactic medium could be associated with the collapse of protogalaxies are shown to be consistent with the observations. Any discrete source model for the origin of the radiation would require more than 100 times as many sources as there are galaxies.\r\n" }, { "name": "Reid, Mark Jonathan", "degree": "PhD", "year": "1976", "title": "The Structure of Hydroxyl Masers and Circumstellar Envelopes of Long Period Variable Stars", "advisor": "Muhleman, Duane Owen", "url": "https://resolver.caltech.edu/CaltechETD:etd-08262008-113619", "creators": [ { "name": { "family": "Reid", "given": "Mark Jonathan" }, "id": "Reid-Mark-Jonathan", "orcid": "0000-0001-7223-754X", "display_name": "Reid, Mark Jonathan" } ], "advisors": [ { "name": { "family": "Muhleman", "given": "Duane Owen" }, "id": "Muhleman-D-O", "role": "advisor", "display_name": "Muhleman, Duane Owen" } ], "committee": [ { "name": { "family": "Muhleman", "given": "Duane Owen" }, "id": "Muhleman-D-O", "role": "member", "display_name": "Muhleman, Duane Owen" }, { "name": { "family": "Goldreich", "given": "Peter Martin" }, "id": "Goldreich-P-M", "role": "member", "display_name": "Goldreich, Peter Martin" }, { "name": { "family": "Neugebauer", "given": "Gerry" }, "id": "Neugebauer-G", "role": "member", "display_name": "Neugebauer, Gerry" }, { "name": { "family": "Preston", "given": "George W." }, "id": "Preston-G-W", "role": "member", "display_name": "Preston, George W." }, { "name": { "family": "Cohen", "given": "Marshall H." }, "id": "Cohen-M-H", "role": "member", "display_name": "Cohen, Marshall H." } ], "option_major": [ "plansci" ], "doi": "10.7907/4EGT-TW53", "abstract": "Long period variable stars with envelopes of circumstellar dust and gas often exhibit strong hydroxyl (OH) maser emission. This emission is characterized by two emission line complexes typically separated by 20 km/s. While the OH maser spectra suggest well defined dynamical properties of the circumstellar material, the crucial observations required to determine these properties have been lacking. This thesis is primarily concerned with determining the radial velocity of the central star and the spatial distribution of the maser emission in the circumstellar material.
\r\n\r\nThe radial velocity of the central star can be determined by a statistical analysis of spectral line velocities in an ensemble of stars. Such an analysis is presented in Chapter I for optical emission and absorption lines and for radio OH maser emission lines. The results indicate that, contrary to currently accepted theories, the optical absorption line velocities and the high velocity OH emission line velocities are red-shifted with respect to the stellar radial velocity. This argues against models of the OH emission which involve shock fronts or emission from the limb of a spherically expanding circumstellar shell.
\r\n\r\nThe spatial distribution of the maser emission can be determined from radio interferometric observations. Spectral-line very long baseline (VLB) interferometric observations of the OH maser emission in long period variable stars such as IRC+F10011, U Ori and R Aql are presented in Chapter II. The primary result of these observations is that the apparent sizes of the OH maser components in long period variable stars are greater than or about 5 x 1015 cm. These large apparent sizes argue strongly against either gravitational collapse or rotation as the dominant dynamical process in the circumstellar envelope. Analysis of data obtained on IRC+10011 and VY CMa (discussed in Chapter III) indicate that the two emission complexes probably are separated by distances less than, or comparable to, the extent of the emission in either complex. These and other findings suggest that OH emission from long period variable stars comes from a series of concentric, inhomogeneous, circumstellar shells expanding from the central star. The origin of these shells is probably a result of condensation of dust followed by radiative acceleration away from the star during the stellar light cycle.
\r\n\r\nA direct Fourier inversion of VLB data is presented in Chapter III for the 1612 MHz OH emission of VY CMa. This is the first attempt at such an analysis procedure for any VLB observations. This work demonstrates that Fourier inversion of spectral-line VLB data, even with very limited u-v coverage, is more efficient and less biased than direct model fitting for the resolution of complex source structures.
\r\n" }, { "name": "Chu, Kwong Wah", "degree": "PhD", "year": "1975", "title": "HI Observations of Dust Clouds", "advisor": "Rogstad, David Herbert", "url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-081132", "creators": [ { "name": { "family": "Chu", "given": "Kwong Wah" }, "id": "Chu-Kwong-Wah", "display_name": "Chu, Kwong Wah" } ], "advisors": [ { "name": { "family": "Rogstad", "given": "David Herbert" }, "id": "Rogstad-D-H", "role": "advisor", "display_name": "Rogstad, David Herbert" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/FFYW-J027", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAperture synthesis observations of three dust clouds, L134, L1495 and L1517, were made at 21 cm. A 7 arc min diameter beam was synthesized, and the velocity resolution was 0.2 km/sec. In addition to interferometer observations, single dish measurements were carried out to provide large scale information. Two dust clouds, L134 and L1495, were detected in absorption against background 21 cm emission. In both cases the 21 cm absorption line is at a velocity coincident with molecular lines detected in the dust clouds. The hydrogen responsible for the absorption line has a spin temperature less than 2[...] K, and the columnar atomic hydrogen density through the dust clouds is between [...] and [...]. Based upon optical extinction and normal cosmic abundances, the expected hydrogen content is [...]. It is presumed that most of the hydrogen is in molecular form.\r\n\r\nL134 consists of two velocity components separated by 2 km/sec. Fragmentation of a larger cloud into two smaller components may explain the data, but more evidence is needed to draw any firm conclusion. Within an individual velocity component, no significant substructure was detected in L134 or L1495. The optical appearance of L1517 strongly suggests a fragmented structure, but this dust cloud was not detectable at 21 cm. L1517 may be sufficiently dense that the amount of residual atomic hydrogen is too small to detect, but this conjecture remains to be substantiated.\r\n" }, { "name": "Bieging, John Harold", "degree": "PhD", "year": "1974", "title": "Aperture Synthesis Observations of OH Absorption in the Galactic Center", "advisor": "Seielstad, George A.; Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09292005-082550", "creators": [ { "name": { "family": "Bieging", "given": "John Harold" }, "id": "Bieging-John-Harold", "display_name": "Bieging, John Harold" } ], "advisors": [ { "name": { "family": "Seielstad", "given": "George A." }, "id": "Seielstad-G-A", "role": "advisor", "display_name": "Seielstad, George A." }, { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/HD0Q-HN74", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe galactic center radio sources Sgr A and Sgr B2 have been mapped, by an aperture synthesis technique, in the 1667 MHz absorption line of the OH molecule. The angular resolution of the maps is [...] and the velocity resolution is 1.44 km [...]. The range of velocities covered by the maps is from -200 to +100 km [...] in the local standard of rest. The data are presented in two forms: (i) spectra of brightness temperature as a function of velocity, for fixed positions in right ascension and declination; and (ii) maps of the optical depth distribution in the spatial coordinates, for fixed velocity.\r\n\r\nThe deep absorption line at +40 km [...] in Sgr A is produced by two separate components. Both components appear to be very massive, dense clouds undergoing rapid rotation about axes perpendicular to the galactic plane. If the clouds are gravitationally bound, then their total masses must exceed [...].\r\n\r\nFifteen discrete molecular clouds are seen in absorption against Sgr B2 over a velocity range from -120 km [...] to +100 km [...]. The strong absorption feature at +60 [...] is resolved into four separate clouds, which are closely associated with the HII region GO.7-0.0. It is suggested that the ionized gas and the dense molecular clouds may be interacting dynamically to produce the observed difference in velocity between the [...] recombination line and the OH absorption lines.\r\n\r\nThe implications of these observations for various kinematical models of the galactic center are discussed. Simple models with one or two expanding and rotating rings are not adequate to explain the data.\r\n\r\nThe excitation temperature of the OH 1667 MHz transition is less than 10K, based on the maximum line temperature away from the continuum sources. However, one anomalous region north of G0.7-0.0 shows apparently thermal line emission, which implies an excitation temperature between 30K and 80K if the gas is optically thick. The thermal emission has a maximum angular extent of 12 arcminutes.\r\n\r\nThe molecular clouds fall into two groups. Those with positive radial velocities have linewidths which are, on-the average, twice as large as those for clouds with negative radial velocities. The positive-velocity clouds tend to have larger optical depths and column densities of OH. The mean value of [...] for the positive-velocity clouds is [...] , while for negative-velocity clouds, the mean is [...]. For an assumed excitation temperature of 10K, the space densities of OH molecules exceed by at least an order of magnitude the expected densities based on a theoretical model for the reaction rates of molecule formation. The parameters of the theoretical model may be inappropriate for the galactic center region." }, { "name": "Shaffer, David Bruce", "degree": "PhD", "year": "1974", "title": "The Structure of Compact Radio Sources at 10.7 GHz", "advisor": "Cohen, Marshall H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-06112008-140732", "creators": [ { "name": { "family": "Shaffer", "given": "David Bruce" }, "id": "Shaffer-David-Bruce", "display_name": "Shaffer, David Bruce" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Marshall H." }, "id": "Cohen-M-H", "role": "advisor", "display_name": "Cohen, Marshall H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/FER5-8H88", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nVery long baseline interferometry has been used to study the compact structure of seven radio sources at 10709 MHz ([...] = 2.8 cm). The observations, the first of a series, were made on April 28 - May 1, 1972, using the NRAO Mark II recording system. Antennas of the Owens Valley Radio Observatory (California), the Harvard Radio Astronomy Station (Texas), and the National Radio Astronomy Observatory (West Virginia) were used to give three baselines that greatly improved the (u,v)-plane coverage compared to the coverage of previously used single baselines. The three baselines had lengths of 119, 84, and 54x10[...] [...].\r\n\r\nThe observed sources were 3C 84, NRAO 150, OJ 287, 4C 39.25, 3C 273, PKS 2134+004, and VRO 42.22.01 (BL Lac). They were tracked by all three antennas during the time of mutual visibility, giving 8 to 11.5 hours of continuous coverage. With the maximum baseline of 119x10[...] [...] and a u-v cell size of ~40x10[...] [...], it is unlikely that we have missed any important structure information in the range 0[...]0005 to 0[...]005.\r\n\r\nFourier inversion of the observations was impossible because there was no phase calibration, and model fitting procedures were used to interpret the data. For five of the sources (NRAO 150, OJ 287, 4C 39.25, 3C 273, and VRO 42.22.01) models were found that fit the observations quite well. For 3C 84 and PKS 2134+004 no simple model could be found, but a rough idea of the source structure was still possible. For most of the sources, interferometric results at other frequencies and resolutions are consistent with the present findings, and a joint interpretation is given.\r\n\r\nFor all the sources except OJ 287 (which looks like a point source at our resolution and was used to calibrate the correlated flux density scale) and possibly NRAO 150, two or more separate components are required to match the observations. Component separations range from 0[...]0006 to 0[...]005 and their sizes from [...]0[...]0003 to ~0[...]002. Components less than ~0[...]002 contribute 0.85 or more of the total 10.7 GHz flux density for all the sources. Assuming synchrotron self-absorbed components, the magnetic fields in the compact sources are %10-3\u00b11 gauss. This value is less than the equi-partition field, and the individual components are expected to expand from particle pressure.\r\n\r\nSuggestions are given for additional observations to improve our knowledge of the structure and nature of compact sources." }, { "name": "Greisen, Eric Winslow", "degree": "PhD", "year": "1973", "title": "Aperture Synthesis of Interstellar Neutral Hydrogen in Absorption", "advisor": "Cohen, Marshall H.; Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08252008-150426", "creators": [ { "name": { "family": "Greisen", "given": "Eric Winslow" }, "id": "Greisen-Eric-Winslow", "display_name": "Greisen, Eric Winslow" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Marshall H." }, "id": "Cohen-M-H", "role": "advisor", "display_name": "Cohen, Marshall H." }, { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/3A2K-C664", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe Owens Valley Radio Observatory interferometer has been used to carry out a program of aperture synthesis in the interstellar neutral hydrogen line. Maps having resolutions of 1 KHz and about 1.3 arc minutes have been produced using a novel Fourier inversion procedure which is discussed in some detail. The equipment, observing procedure, noise, and gaussian analysis of spectra are also treated.\r\n\r\nThe Perseus arm feature in the spectrum of Cygnus A is of low optical depth but reveals considerable spatial structure. The data suggest that the hydrogen is located in a thin shell expanding at 2 km/sec, with a radius around 9.7 parsecs and a total mass of 175 solar masses. The Perseus arm feature in the spectrum of Cassiopeia A contains very large amounts of hydrogen with extremely complicated spatial structure. The results may be explained qualitatively by the two-arm spiral shock model of the Galaxy. The principal component in the spectrum of the Crab Nebula is found to show a considerable velocity gradient across the source and appears to contain several condensations within a large, less dense cloud. The absorption feature in the spectrum of 3C353 appears to have a gradient in the dispersion of one component. If real, this result suggests scale lengths in the interstellar hydrogen as small as 0.14 parsecs. The absorption spectra of W12, 3C147, Cygnus A (local arm), and 3C123 are also discussed briefly.\r\n\r\nUpper limits to the temperature as low as 50\u00b0K are found for some of the spectral components although upper limits between 80 and 160\u00b0K are more common. Hydrogen clouds with diameters about 1 parsec and densities on the order of 100 cm[\u2026] are shown to be common. The implications of these results for the two-phase model of the interstellar medium are discussed.\r\n" }, { "name": "Purcell, George Harber", "degree": "PhD", "year": "1973", "title": "The Structure of Compact Radio Sources at 606 MHz", "advisor": "Cohen, Marshall H.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08212008-100027", "creators": [ { "name": { "family": "Purcell", "given": "George Harber" }, "id": "Purcell-George-Harber", "display_name": "Purcell, George Harber" } ], "advisors": [ { "name": { "family": "Cohen", "given": "Marshall H." }, "id": "Cohen-M-H", "role": "advisor", "display_name": "Cohen, Marshall H." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/8jjw-z848", "abstract": "Long-baseline interferometry has been used to study the structure of thirteen compact radio sources at 606 MHz. The baseline was 3324 kilometers long and nearly east-west in orientation, so that the maximum angular resolution was about a hundredth of a second of arc for each source.\r\n\r\nThere were two series of observations, made on June 29 to July 1, 1971, and February 3 to 6, 1972. For most of the sources observed in each session, the correlated flux was measured from ten to forty times over a wide range of hour angle, with a standard error for each measurement of about 0.12 flux unit. A few sources were observed less often. Simple source models were then fitted to the data and compared to the models proposed by other observers.\r\n\r\nThe data for most of the sources were found to be consistent with models containing an elliptical halo concentric with an unresolved core. 3C 147, 3C 273, and 3C 279 appear to be more complicated, however. The observations of 3C 84, 3C 279, and 3C 345 also show evidence of weak structure at relatively large distances from the strong central components.\r\n\r\nP1345+12 and CTD 93 were observed only in the first session, and 3C 120 and 3C 286 only in the second session. CTA 21, 3C 84, 3C 147, 3C 273, 3C 279, 3C 345, 3C 380, CTA 102, and 3C 454.3 were observed in both sessions, and all but CTA 21 and 3C 380 gave strong evidence of changes in flux or structure during the interim. These changes appear to be intrinsic to the sources, and not the result of instrumental effects or scintillation phenomena.\r\n" }, { "name": "Wright, William Edwin", "degree": "PhD", "year": "1973", "title": "Polarization Observations of 3C Radio Sources and Galactic Faraday Rotation", "advisor": "Seielstad, George A.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272008-135404", "creators": [ { "name": { "family": "Wright", "given": "William Edwin" }, "id": "Wright-William-Edwin", "display_name": "Wright, William Edwin" } ], "advisors": [ { "name": { "family": "Seielstad", "given": "George A." }, "id": "Seielstad-G-A", "role": "advisor", "display_name": "Seielstad, George A." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "physics" ], "doi": "10.7907/ZQYY-S826", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe linear polarization properties of 206 radio sources from the 3CR Catalogue have been measured--in most cases at 21, 18 and 6 cm. The observing scheme also allowed the establishement of upper limits for the degree of circular polarization. The Owens Valley Radio Observatory 90' interferometer was used for these observations, and it operated with the many advantages of a crossed-feed interference polarimeter over a single-dish system.\r\n\r\nWith the use of all available data, the Faraday rotation measures of 354 radio sources, mostly extragalactic, have been computed with careful attention to ambiguities and uncertainties; a novel quality grading system has been employed. These rotation measures constitute a powerful probe of the magnetic field structure and electron density of the local spiral arm. If the electrons in the local regions of the galaxy form a disk 200 pc in thickness and 2 kpc in radius , then there is a uniform\tlinear component of the galactic field in the direction 1 = 94[degress] [...] 3[degrees], b = -8[degrees] [...] 8[degrees] with a strength of n[subscript e]B = 0.12 electrons-cm[superscript -3]-[mu]guass, or B = 2.0 [mu]gauss for n[subscript e] = 0.06 cm[superscript]-3. Distributions of the differences between this model and the actual rotation measures show that regions of magnetic loops and field reversals or electron concentrations of 100 to 200 pc in size have values of n[subscript e]B two to three times that of the average linear field of the model, implying a high degree of disorder. Most of the very large rotation measures seem to be produced by small scale structure in the galaxy, although a very few may be intrinsic to the source. The linear field model compares well with hydrogen line Zeem splitting, pulsar dispersion and rotation measures, and other magnetic field data. The apparent discrepancy with field structures given by stellar polarization can be resolved by differences in the distributions of electrons and dust and by the large-scale loops and field reversals.\r\n\r\nSearches for correlations between rotation measure and source type, depolarization, or redhsift have all led to negative results. The upper limit for a uniform, linear component of the intergalactic magnetic field, based on the failure of the last correlation, is n[subscript e]B < 2 x 10[superscript -13] cm[superscript -3] gauss.\r\n" }, { "name": "Shostak, Gerson Seth", "degree": "PhD", "year": "1972", "title": "Aperture Synthesis Observations of Neutral Hydrogen in Three Galaxies", "advisor": "Moffet, Alan Theodore; Schmidt, Maarten; Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08212008-102427", "creators": [ { "name": { "family": "Shostak", "given": "Gerson Seth" }, "id": "Shostak-Gerson-Seth", "display_name": "Shostak, Gerson Seth" } ], "advisors": [ { "name": { "family": "Moffet", "given": "Alan Theodore" }, "id": "Moffet-A-T", "role": "advisor", "display_name": "Moffet, Alan Theodore" }, { "name": { "family": "Schmidt", "given": "Maarten" }, "id": "Schmidt-M", "role": "advisor", "display_name": "Schmidt, Maarten" }, { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/FRRJ-YB73", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAperture synthesis techniques have been used to study the three galaxies NGC2403 (Scd), NGC4236 (SBdm), and IC10 (Irr) in the 21-cm line of neutral hydrogen and off-line continuum. Spatial resolution was 2 minutes of arc; velocity resolution was 21 km-s[...]. The data yield information on the distribution of the HI, and its associated velocity field.\r\n\r\nHydrogen extent of the objects agrees well with their optical size, and evidences a lumpy structure. HI peaks occur away from the nuclei for NGC2403 and NGC4236, and are suggestive of a ring structure for the former galaxy. The hydrogen distribution of IC10 is similar in appearance to that of the Small Magellanic Cloud. In all objects HI peaks show good positional agreement with major HII regions.\r\n\r\nVelocity fields are derived for all objects, and rotation curves obtained for NGC2403 and NGC4236. These curves evidence differential rotation but do not include Keplerian tails, implying that the mass distributions are considerably extended and the total masses poorly determined. The velocity field of IC10 suggests rotation.\r\n\r\nNon-circular motions of ~10 km-s[...] are seen in NGC2403, and these agree well with the streaming motions predicted by the density-wave theory of spiral structure.\r\n\r\nA comparison of NGC2403 with the late-type spirals M33 and M101 reveals a progressive deepening of the central HI depression with increasing mass. Rotation curves for these three galaxies are similar, and consequently all are expected to have mass-to-light ratios which increase rapidly with radius. All have similar maximum HI surface densities (~10[...] atoms-cm[...]) and observed fractional hydrogen masses (~9%).\r\n" }, { "name": "Yip, Ka Bing Winson", "degree": "PhD", "year": "1972", "title": "Synthesis of the Polarization Properties of Cygnus A at 8300 and 9600 Megahertz", "advisor": "Seielstad, George A.; Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08252008-075815", "creators": [ { "name": { "family": "Yip", "given": "Ka Bing Winson" }, "id": "Yip-Ka-Bing-Winson", "display_name": "Yip, Ka Bing Winson" } ], "advisors": [ { "name": { "family": "Seielstad", "given": "George A." }, "id": "Seielstad-G-A", "role": "advisor", "display_name": "Seielstad, George A." }, { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/GVT6-PD26", "abstract": "Methods of polarized interferometry have been used in conjunction with the earth rotation aperture synthesis technique to study the polarized intensity distributions of Cygnus A at 8300 MHz and 9600 MHz. The total intensity distribution at 8300 MHz has also been obtained.\r\n\r\nAlthough the resolutions obtained in these observations are about 20\", it is still quite insufficient to reveal the structures in the components for a detailed comparison with the theoretical model proposed by Mills and Sturrock. The general featere of the ram pressure confinement mechanism, however, is consistent with this observation.\r\n\r\nThe polarized distributions yield a rather fast variation of large rotation measures across the east component. There is also a reversal of the longitudinal magnetic field in the direction of the west component. Correlations with the distribution of small hydrogen clouds deduced from HI absorption measurements have been discussed.\r\n\r\nThere seems to be little depolarization across this source except in the bridge, and this is believed to be occurring outside of the emitting region. However, no detailed models can be worked out without further information about the conditions of the intervening medium.\r\n" }, { "name": "Sramek, Richard Anthony", "degree": "PhD", "year": "1970", "title": "The Brightness Distribution of Core-Halo Radio Sources", "advisor": "Moffet, Alan Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-05092008-133654", "creators": [ { "name": { "family": "Sramek", "given": "Richard Anthony" }, "id": "Sramek-Richard-Anthony", "display_name": "Sramek, Richard Anthony" } ], "advisors": [ { "name": { "family": "Moffet", "given": "Alan Theodore" }, "id": "Moffet-A-T", "role": "advisor", "display_name": "Moffet, Alan Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/3HJ1-PE18", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe east-west visibility of 28 extragalactic radio sources with both large and very small components was obtained at 605 MHz using the radio interferometer at the Owens Valley Radio Observatory. A 2' HPBW fan beam was synthesized from observations made at twelve spacings between 62 and 977 wavelengths. The availability of such low spatial frequencies permitted the calculation of the brightness distribution of components as large as 56'. The brightness distributions of the following galaxies are plotted: (spiral galaxies) P0045-25, P1302-49 P1334-29, (elliptical galaxies) 3C40, 3C105, P0843-33, 3C236, 3C247, 3C264, P1216-10, 3C274, 3C287.1, 3C293, and P2247+11.\r\n\r\nFourteen of the observed sources had a core-halo or asymmetric double structure and had their large components well resolved at the 977[...] spacing. The spectral indices of the large and small components of these sources were obtained by comparing the flux densities given here with those at other frequencies. The spectra of the large components are generally steeper than those of the small components with an average difference of spectral indices of [...] = +0.3.\r\n\r\nAssuming equipartition of magnetic and particle energies the total energies of the large halos are ~ [...] ergs. This is sufficient energy to maintain the current radio luminosities for ~ [...] years.\r\n\r\nThree of these fourteen sources have a core-halo structure and are associated with spiral galaxies; the remaining eleven are associated with elliptical galaxies. Two of the remaining sources are asymmetric doubles, and nine have a core-halo structure. Four of the core-halo sources have simple halos, two have double halos, and three have an undetermined halo structure. The ratio of observed double to simple halos can be explained by the projection of double halos randomly oriented in three dimensions provided the ratio of component separation to diameter, R, is less than two. Since doubles without a core have R between two and four, the mechanism of radio galaxy formation is likely to produce a core for low values of R. From the present investigation it is impossible to conclude whether there exists a class of core-halo radio galaxies with simple halos (R [...] 1) or whether the observed core-halo objects represent the low-R end of the ensemble of double radio sources.\r\n" }, { "name": "Weiler, Kurt Walter", "degree": "PhD", "year": "1970", "title": "Synthesis of the Polarization Properties of 3C10 and 3C58 at 1420 and 2880 Megahertz", "advisor": "Seielstad, George A.; Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08212008-112732", "creators": [ { "name": { "family": "Weiler", "given": "Kurt Walter" }, "id": "Weiler-Kurt-Walter", "display_name": "Weiler, Kurt Walter" } ], "advisors": [ { "name": { "family": "Seielstad", "given": "George A." }, "id": "Seielstad-G-A", "role": "advisor", "display_name": "Seielstad, George A." }, { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "physics" ], "doi": "10.7907/9EJC-C589", "abstract": "An earth rotation aperture synthesis technique was combined with the methods of interference polarimetry to study the total intensity and polarization properties of the two radio sources 3C10 and 3C58 with a resolution of approximately one minute of arc at both 1420 and 2880 MHz. These data were then used to calculate the spectral index, rotation measure, intrinsic position angle, and depolarization distributions for the two sources. Source models were constructed and estimates obtained for the internal magnetic field strength and relativistic electron density. The origins of the rotation measure and depolarization were studied and estimates of the internal thermal electron density obtained. Attempts were made to compare the present results with the several theories of supernova remnants.\r\n\r\n3C10, the remnant of a Type I supernova, in the total radiation is an annular source with a sharp outer edge and little emission from the central regions. The polarized flux density distribution has a similar, but less well defined, ring shape which exhibits a relatively high degree of polarization in many areas. The intrinsic position angle distribution implies a radial component of the magnetic field. 3C58, also believed to be the remnant of a Type I supernova, has a simple shape in the total radiation, brightest in the center and falling off slowly to zero on the edges with an elongation in the east-west direction. The polarized emission shows considerable structure having many areas with relatively high degrees of polarization. The intrinsic position angle distribution implies the existence of a component of the magnetic field lying parallel to the major east-west axis over the full extent of the source.\r\n" }, { "name": "Fomalont, Edward Berel", "degree": "PhD", "year": "1967", "title": "The East-West Structure of Radio Sources at 1425 MHz", "advisor": "Moffet, Alan Theodore", "url": "https://resolver.caltech.edu/CaltechETD:etd-04302008-153110", "creators": [ { "name": { "family": "Fomalont", "given": "Edward Berel" }, "id": "Fomalont-Edward-Berel", "display_name": "Fomalont, Edward Berel" } ], "advisors": [ { "name": { "family": "Moffet", "given": "Alan Theodore" }, "id": "Moffet-A-T", "role": "advisor", "display_name": "Moffet, Alan Theodore" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/W9HN-MY72", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe east-west radio structures of 532 sources have been obtained with the Caltech variable spacing interferometer at a frequency of 1425 MHz. The visibility functions, measured at nine interferometer spacings between 144[...] and 2626[...], are presented in tabular form for all of the sources. The east-west source structures were calculated by a model fit of the data or by a direct numerical inversion of the data.\r\n\r\nThe statistics of the radio structures have been analyzed. There are three major structure types: simple double, halo-core and triple. The simple double sources have two distinct components of emission having nearly equal intensities and diameters with the radio galaxy lying at the center of the two components in most cases. The halo-core sources consist of a small radio core, usually complex, coincident with the radio galaxy and a much larger region of emission, the halo, not necessarily symmetrically disposed around the radio core. The triple and more complex sources are discussed briefly and it is suggested that many are genetically related to double and halo-core sources.\r\n\r\nOther results from the observations are: a slight correlation of the radio and optical structure of galaxies; a difference for the N-S relationship of quasars and radio galaxies based on their statistical separation by brightness temperature; a model for the evolution of a double source in which the component separation increases at five times the rate of the expansion of the component diameters; the lack of simple sources characterized by one main region of emission; and the suggestion that 3C120 and 3C236 are involved in a violent explosion.\r\n" }, { "name": "Rogstad, David Herbert", "degree": "PhD", "year": "1967", "title": "Rotation and Masses of Galaxies as Determined by Single Spacing Interferometry of 21 cm Hydrogen Emission", "advisor": "Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-10012002-152156", "creators": [ { "name": { "family": "Rogstad", "given": "David Herbert" }, "id": "Rogstad-David-Herbert", "display_name": "Rogstad, David Herbert" } ], "advisors": [ { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "physics" ], "doi": "10.7907/PV8N-N966", "abstract": "A total of 79 galaxies have been investigated with the Owens Valley Observatory's two-element interferometer for content of neutral hydrogen. The baseline used was 100 feet east-west, and the filter bandwidth was 100 kHz. Thirty of the galaxies had detectable emission (> 0.5 f.u.). The results are presented as line and position profiles for each galaxy (i.e.plots of the flux, and its position derived from the interferometer phase as a function of radial velocity).\r\n\r\nAn extensive investigation of model profiles is also presented for the purposes of interpretation of the observed results. It is shown that while in most cases the position profile cannot be directly interpreted as the rotation curve, the model analysis does suggest a method for estimating the rotational characteristics of the galaxies from the profiles.\r\n\r\nUsing the estimated rotational parameters, total masses were calculated and are presented along with other quantities derivable from the profiles, such as the galaxy radial velocities and estimates of the neutral hydrogen masses.\r\n\r\nAll of the irregular galaxies that were detected were found to be rotating, with the exception of WLM, which was inconclusive." }, { "name": "Berge, Glenn LeRoy", "degree": "PhD", "year": "1965", "title": "An Interferometric Study of Jupiter's Decimeter Radio Emission", "advisor": "Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09122002-090152", "creators": [ { "name": { "family": "Berge", "given": "Glenn LeRoy" }, "id": "Berge-Glenn-LeRoy", "display_name": "Berge, Glenn LeRoy" } ], "advisors": [ { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/QYHG-PN18", "abstract": "NOTE: Text or symbols not rederable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nAn interferometric study of the decimeter radio emission from the planet Jupiter has recently been carried out at the Owens Valley Radio Observatory. Using the two 90-foot paraboloids as an interference polarimeter, observations have been made with various eastwest spacings ranging from 300 to [.......] at 10.4 cm. and 300 to [......] at 21.2 cm. and also with some critical north-south spacings at 10.4 cm.\r\n\r\nThe visibility functions obtained are consistent with earlier measurements, which gave the polar and equatorial dimensions as one and three planetary diameters respectively, but they are more complete and extend to larger baselines. They permit the fitting of a rather detailed model for the decimeter brightness distribution. The observations are consistent with a symmetrical synchrotron emission source having the polarization properties one would expect with a dipole magnetic field. It probably is centered quite closely on the planetary disk, which is itself seen as a thermal radio source.\r\n\r\nThe observations also indicate the presence of a small circularly polarized component in the radiation which varies in magnitude and sense as Jupiter rotates. Another result is that the disk emission at 10.4 cm. is about twice the thermal emission one would expect for a temperature of 130 [degrees] K.\r\n\r\nThe implications of the various results are discussed." }, { "name": "Clark, Barry Gillespie", "degree": "PhD", "year": "1964", "title": "The Twenty-One Centimeter Hydrogen Line in Absorption", "advisor": "Schmidt, Maarten; Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-09112002-180017", "creators": [ { "name": { "family": "Clark", "given": "Barry Gillespie" }, "id": "Clark-Barry-Gillespie", "display_name": "Clark, Barry Gillespie" } ], "advisors": [ { "name": { "family": "Schmidt", "given": "Maarten" }, "id": "Schmidt-M", "role": "advisor", "display_name": "Schmidt, Maarten" }, { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/385M-0W22", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe brightness distributions across five intense radio sources have been investigated in the hydrogen line absorption features. In some cases there has been found a variation of the absorption across the face of a source, which, with the kinematical distance to the cloud in question, allowed a typical length to be estimated, which in turn allows estimations of densities and masses. Densities range from a few atoms per cubic centimeter, to, in the case of a small cloud in front of Orion A, as much as 700 atoms per cubic centimeter. Masses range from a few solar masses up to perhaps a thousand solar masses in the cloud causing the deep line in Cas A.\r\n\r\nThe absorption profiles of the bright sources were analysed into Gaussian components, allowing parameters to be quoted for individual clouds, and, in a few cases, allowing an interesting upper limit to the temperature to be set from the dispersions of the separated components.\r\n\r\nThe absorption features in several other sources were briefly investigated, including three absorption spectra never before published, and new upper limits for the absorption of apparently unabsorbed sources were set in six cases. This material is briefly analysed statistically, from which it is concluded that the distribution law for central optical depths is approximately [...] and that a line of sight, on the average, intersects 4.1 clouds per kiloparsec in the galactic plane. There is some evidence that the density is about twice this in the local spiral arm.\r\n\r\nSome evidence is presented in favor of a \"raisin pudding\" model of the interstellar medium, in which clouds with temperatures of less than a hundred degrees supply all absorption, and most of the hydrogen line emission, while an appreciable part of the emission profiles is due to a hot intercloud medium of neutral hydrogen, at a temperature of several thousand degrees, and a density of about one half atom per cubic centimeter." }, { "name": "Kellermann, Kenneth Irwin", "degree": "PhD", "year": "1963", "title": "The Spectra of Galactic and Extragalactic Radio Sources", "advisor": "Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04122004-164144", "creators": [ { "name": { "family": "Kellermann", "given": "Kenneth Irwin" }, "id": "Kellermann-Kenneth-Irwin", "display_name": "Kellermann, Kenneth Irwin" } ], "advisors": [ { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "physics" ], "doi": "10.7907/2CYZ-PE61", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
\r\n\r\nObservations have been made of the flux density of a number of discrete radio sources at 475, 710, 958, 1420, 2841, and 3200 Mc, using the two-element interferometer of the California Institute of Technology Radio Observatory. These have been combined with similar measurements at other frequencies made by different observers, to determine the spectral distribution for 242 sources where data is available over a wide range of frequencies.
\r\n\r\nIt is shown that the spectra of most sources can be closely approximated by a simple power law of the form [...], at least between 38 and 1420 Mc. For these sources, the distribution of spectral indices is sharply peaked about a mean value of -0.77 with 50 per cent of the sources having an index between -0.70 and -0.85. No sources were found with an index steeper than -1.23. In most cases, the spectral index is a function of frequency over the observed range from 38 to 3200 Mc. For these sources, which generally have a high surface brightness, the typical change in spectral index is about 0.5 in the sense that the spectrum is flatter at longer wavelength.
\r\n\r\nThe observed spectral distributions are interpreted in terms of synchrotron radiation and it is postulated that the bright sources having a curved spectrum are relatively young and rapidly evolving toward a power law spectrum.
" }, { "name": "Seielstad, George Andrew", "degree": "PhD", "year": "1963", "title": "Measurements of the Linear Polarization of Radio Sources at Decimeter Wavelengths", "advisor": "Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08282008-082654", "creators": [ { "name": { "family": "Seielstad", "given": "George Andrew" }, "id": "Seielstad-George-Andrew", "display_name": "Seielstad, George Andrew" } ], "advisors": [ { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "physics" ], "doi": "10.7907/HY16-8F63", "abstract": "Measurements at three frequencies of the degree and preferred orientation of the linearly polarized radiation from twenty-five unresolved radio sources are reported. The frequencies used were 2840 Mc/s, 1666 Mc/s, and 1420 Mc/s. The results are combined with those of other observers in order to derive properties of the emitting sources and of the Galaxy. An interferometric technique for determining the distribution of polarized radiation within a radio source is developed and applied to a few sources. Calculations on some model source distributions are included.\r\n" }, { "name": "Read, Richard Bradley", "degree": "PhD", "year": "1962", "title": "Accurate Declination Measurements of Radio Sources", "advisor": "Bolton, John G.; Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-08272008-092141", "creators": [ { "name": { "family": "Read", "given": "Richard Bradley" }, "id": "Read-Richard-Bradley", "display_name": "Read, Richard Bradley" } ], "advisors": [ { "name": { "family": "Bolton", "given": "John G." }, "id": "Bolton-J-G", "role": "advisor", "display_name": "Bolton, John G." }, { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "physics" ], "doi": "10.7907/MDXD-QD10", "abstract": "The two 90-foot steerable paraboloids of the Owens Valley Radio Observatory were used as a two-element interferometer at 960 Mc/s with various separations along a north-south baseline to measure accurately the declinations of a number of radio sources most of which were of small diameter. The measured values of declination are tabulated for 110 sources with right ascensions between 0 hours and 14 hours 10 minutes. The standard errors of the measured values range from 2.6 seconds of arc to 46 seconds of arc with an average of 13 seconds of arc. A discussion of the sources of error is included." }, { "name": "Wilson, Robert Woodrow", "degree": "PhD", "year": "1962", "title": "Observations of the Galactic Plane at 960 Mc/s", "advisor": "Bolton, John G.; Schmidt, Maarten", "url": "https://resolver.caltech.edu/CaltechETD:etd-04012003-131925", "creators": [ { "name": { "family": "Wilson", "given": "Robert Woodrow" }, "id": "Wilson-Robert-Woodrow", "display_name": "Wilson, Robert Woodrow" } ], "advisors": [ { "name": { "family": "Bolton", "given": "John G." }, "id": "Bolton-J-G", "role": "advisor", "display_name": "Bolton, John G." }, { "name": { "family": "Schmidt", "given": "Maarten" }, "id": "Schmidt-M", "role": "advisor", "display_name": "Schmidt, Maarten" } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "physics" ], "doi": "10.7907/1R1X-J090", "abstract": "A survey of the radio radiation at 960 Mc/s from the part of the plane of the Galaxy with declination above 48\u00b0 has been made. 112 discrete sources were found in the region studied. The positions, intensities, and sizes of these sources have been catalogued, and a search for optical identifications made. The broadly distributed radiation is interpreted in terms of a space distribution of ionized hydrogen and of emissivity from synchrotron emission." }, { "name": "Harris, Daniel Everett", "degree": "PhD", "year": "1961", "title": "The Continuous Spectra of Radio Sources with Particular Reference to Non-Thermal Galactic Sources", "advisor": "Stanley, Gordon J.; Bolton, John G.", "url": "https://resolver.caltech.edu/CaltechETD:etd-03232006-111338", "creators": [ { "name": { "family": "Harris", "given": "Daniel Everett" }, "id": "Harris-Daniel-Everett", "display_name": "Harris, Daniel Everett" } ], "advisors": [ { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." }, { "name": { "family": "Bolton", "given": "John G." }, "id": "Bolton-J-G", "role": "advisor", "display_name": "Bolton, John G." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "astronomy" ], "doi": "10.7907/N09S-3J04", "abstract": "960 Mc observations of over 400 sources are reported in two parts. Part I contains position and intensity measurements of 106 sources (chiefly taken from the recent Cambridge surveys), and the results of 376 intensity measurements of sources previously observed at Sydney. Spectral indices are derived from the intensity measurements and the previous investigator's observations. The resulting spectral index distribution has a median value of -0.65 \u00b1 0.10 and a dispersion such that 75% of the values lie within 0.25 of the median. Galactic sources show a larger dispersion of spectral index than do the sources assumed to be external galaxies.
\r\n\r\nPart II is based on 960 Mc observations of extended galactic nebulae, usually identified with supernova remnants. Contour diagrams of antenna temperature are presented for four of the larger objects. A detailed study of the Cygnus Loop shows that the radio emission is chiefly non-thermal, with a spectral index of -0.1 \u00b1 0.1. An attempt to detect linear polarization places an upper limit of 30% for selected regions of the Cygnus Loop. Spectral indices ranging from -0.8 to +0.5 are derived for 12 other sources. Calculations show that the occurrence of optical synchrotron radiation is not ruled out by existing observations. An empirical relation between spectral index and physical size of supernova remnants suggests that the energy spectrum of relativistic particles flattens with age. A possible mechanism for this behavior is considered.
" }, { "name": "Moffet, Alan Theodore", "degree": "PhD", "year": "1961", "title": "Interferometric Measurement of Brightness Distributions in Discrete Radio Sources", "advisor": "Bolton, John G.; Leighton, Robert B.; Stanley, Gordon J.", "url": "https://resolver.caltech.edu/CaltechETD:etd-04212006-170658", "creators": [ { "name": { "family": "Moffet", "given": "Alan Theodore" }, "id": "Moffet-Alan-Theodore", "display_name": "Moffet, Alan Theodore" } ], "advisors": [ { "name": { "family": "Bolton", "given": "John G." }, "id": "Bolton-J-G", "role": "advisor", "display_name": "Bolton, John G." }, { "name": { "family": "Leighton", "given": "Robert B." }, "id": "Leighton-R-B", "role": "advisor", "display_name": "Leighton, Robert B." }, { "name": { "family": "Stanley", "given": "Gordon J." }, "id": "Stanley-G-J", "role": "advisor", "display_name": "Stanley, Gordon J." } ], "committee": [ { "name": { "family": "Unknown", "given": "Unknown" }, "display_name": "Unknown, Unknown" } ], "option_major": [ "physics" ], "doi": "10.7907/QCM3-7524", "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nInformation about the brightness distributions in 110 extragalactic and 17 galactic radio sources has been obtained from observations with the Caltech variable spacing interferometer at a wavelength of 31.3 cm. In these observations, the amplitude and phase of the complex visibility function were measured at transit with antenna spacings of 195[...], 389[...], 779[...], and 1557[...] along an east-west baseline. Using these same basic spacings, and by observing at large hour angles, the visibility amplitude was measured at ten other effective spacings between 126[...] and 1363[...]. Not all sources were observed at all spacings.\r\n\r\nOf the 110 extragalactic sources, 47 are found to have angular diameters greater than [...]. Only 4 of these 47 appear to have smooth, simple structure, while the remaining 43 show some form of complexity, many having two fairly well separated components. It is suggested that the majority of all extragalactic sources have complex structure. For three extragalactic sources (M 87, NGC 5128, and Cygnus A) comparable measurements at other wavelengths have been published, and in each case, significant changes in structure with wavelength are noted.\r\n\r\nThe theory of interferometric investigation of discrete sources is developed in some detail, and previous work in the field is reviewed. Calculations on a number of model sources are described." } ]