For over sixty years scientists have known that a large percentage of heavy elements are created by the rapid neutron-capture process (r-process). However, a clear picture of where the r-process occurs has remained elusive. Many astrophysical origins have been proposed -- each with a range of possible chemical yields and rates. Discovering which origin (or combinations of origins) truly produce the heavy elements we see on Earth is a daunting task.
\r\n\r\nThis thesis seeks to provide observational constraints to pinpoint the dominant origin of the r-process. The majority of this thesis uses Galactic Archaeology to look for r-process signatures in ancient stellar populations (e.g., dwarf galaxies and globular clusters). These ancient stellar populations provide the clearest \"experiments\" to observe how quickly and how much r-process was created. The r-process signature we observe is the amount of barium in individual red giant branch stars in these stellar populations. Chapter 2 discusses how these barium measurements are made from individual extragalactic stars and presents the largest catalog of barium abundances in dwarf galaxies to date.
\r\n\r\nChapter 3 compares the r-process signature -- barium -- to other elements (e.g., magnesium and iron) in the same galaxy to see how the timescale of r-process enrichment compares to the other abundances (whose origins are known). This analysis found that the r-process timescale was more delayed than core-collapse supernovae. This points to neutron star mergers (NSMs) as the dominant source of r-process in the early history of dwarf galaxies.
\r\n\r\nChapter 4 uses a galactic chemical evolution model to test what r-process timescales, yields, and rates are needed to recreate the observations presented in Chapter 2. Preliminary results indicate that NSMs must be included in order for the model to match the observations. In addition, Chapter 4 presents what yield of barium is needed from NSMs to recreate the observations.
\r\n\r\nChapter 5 tests if the stars in the globular cluster M15 were enriched by the r-process after they were born. M15 has an unusual abundance pattern with ~ 1 dex variation in r-process abundances even though most other elements, including iron, do not show a variation. New measurements of barium abundances in main sequence and red giant branch stars of M15 show that the stars were born with their r-process enrichment. This means that an r-process event occurred quickly after the cluster was born -- while it was still forming stars -- and resulted in uneven enrichment.
\r\n\r\nFinally, Chapter 6 presents a solution to one of the technical challenges in locating the sites of r-process nucleosynthesis. Chapter 6 describes how to accurately measure the position and orientation of the CCDs in Zwicky Transient Facility's (ZTF's) camera. ZTF is a transient survey that -- among other science goals -- searches for the electromagnetic counterpart of NSM detections with LIGO. The work included in this chapter increased the survey efficiency of ZTF, which will aid ZTF in localizing transient events, including NSMs. Following up NSMs found by LIGO can provide direct measurements of the amount of r-process material created by NSMs.
\r\n\r\nAltogether, this thesis has made strides to identifying the origin of the r-process. Chapters 3 and 4 identify NSMs as the dominant source of r-process elements in dwarf galaxies. However, Chapter 5 found that globular cluster M15 needs a r-process event to occur quickly -- quicker than is typically expected from a NSM. The observational constraints that have resulted from this thesis provide important clues to where the heaviest elements are made.
", "doi": "10.7907/D0A8-BM50", "publication_date": "2020", "thesis_type": "phd", "thesis_year": "2020" }, { "id": "thesis:9719", "collection": "thesis", "collection_id": "9719", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05142016-213503805", "primary_object_url": { "basename": "yi_cao_2016_thesis.pdf", "content": "final", "filesize": 15900563, "license": "other", "mime_type": "application/pdf", "url": "/9719/1/yi_cao_2016_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Cosmic Explosions: Observations Of Infant Hydrogen-Free Supernovae Towards An Understanding Of Their Parent Systems", "author": [ { "family_name": "Cao", "given_name": "Yi", "orcid": "0000-0002-8036-8491", "clpid": "Cao-Yi" } ], "thesis_advisor": [ { "family_name": "Kulkarni", "given_name": "Shrinivas R.", "clpid": "Kulkarni-S-R" }, { "family_name": "Nugent", "given_name": "Peter E.", "clpid": "Nugent-P-E" } ], "thesis_committee": [ { "family_name": "Cohen", "given_name": "Judith G.", "clpid": "Cohen-J-G" }, { "family_name": "Kulkarni", "given_name": "Shrinivas R.", "clpid": "Kulkarni-S-R" }, { "family_name": "Nugent", "given_name": "Peter E.", "clpid": "Nugent-P-E" }, { "family_name": "Prince", "given_name": "Thomas A.", "clpid": "Prince-T-A" }, { "family_name": "Phinney", "given_name": "E. Sterl", "clpid": "Phinney-E-S" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Radiation in the first days of supernova explosions contains rich information about physical properties of the exploding stars. In the past three years, I used the intermediate Palomar Transient Factory to conduct one-day cadence surveys, in order to systematically search for infant supernovae. I show that the one-day cadences in these surveys were strictly controlled, that the realtime image subtraction pipeline managed to deliver transient candidates within ten minutes of images being taken, and that we were able to undertake follow-up observations with a variety of telescopes within hours of transients being discovered. So far iPTF has discovered over a hundred supernovae within a few days of explosions, forty-nine of which were spectroscopically classified within twenty-four hours of discovery.
\r\n\r\nOur observations of infant Type Ia supernovae provide evidence for both the single-degenerate and double-degenerate progenitor channels. On the one hand, a low-velocity Type Ia supernova iPTF14atg revealed a strong ultraviolet pulse within four days of its explosion. I show that the pulse is consistent with the expected emission produced by collision between the supernova ejecta and a companion star, providing direct evidence for the single degenerate channel. By comparing the distinct early-phase light curves of iPTF14atg to an otherwise similar event iPTF14dpk, I show that the viewing angle dependence of the supernova-companion collision signature is probably responsible to the difference of the early light curves. I also show evidence for a dark period between the supernova explosion and the first light of the radioactively-powered light curve. On the other hand, a peculiar Type Ia supernova iPTF13asv revealed strong near-UV emission and absence of iron in the spectra within the first two weeks of explosion, suggesting a stratified ejecta structure with iron group elements confined to the slow-moving part of the ejecta. With its total ejecta mass estimated to exceed the Chandrasekhar limit, I show that the stratification and large mass of the ejecta favor the double-degenerate channel.
\r\n\r\nIn a separate approach, iPTF found the first progenitor system of a Type Ib supernova iPTF13bvn in the pre-explosion HST archival mages. Independently, I used the early-phase optical observations of this supernova to constrain its progenitor radius to be no larger than several solar radii. I also used its early radio detections to derive a mass loss rate of 3e-5 solar mass per year for the progenitor right before the supernova explosion. These constraints on the physical properties of the iPTF13bvn progenitor provide a comprehensive data set to test Type Ib supernova theories. A recent HST revisit to the iPTF13bvn site two years after the supernova explosion has confirmed the progenitor system.
\r\n\r\nMoving forward, the next frontier in this area is to extend these single-object analyses to a large sample of infant supernovae. The upcoming Zwicky Transient Facility with its fast survey speed, which is expected to find one infant supernova every night, is well positioned to carry out this task.
\r\n", "doi": "10.7907/Z9XD0ZNT", "publication_date": "2016", "thesis_type": "phd", "thesis_year": "2016" }, { "id": "thesis:7784", "collection": "thesis", "collection_id": "7784", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302013-225100503", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 23016889, "license": "other", "mime_type": "application/pdf", "url": "/7784/1/thesis.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "The Relationship Between the Radio and Gamma-Ray Emission of Blazars", "author": [ { "family_name": "Max-Moerbeck Astudillo", "given_name": "Walter Kennerth", "clpid": "Max-Moerbeck-Astudillo-Walter-Kennerth" } ], "thesis_advisor": [ { "family_name": "Readhead", "given_name": "Anthony C. S.", "orcid": "0000-0001-9152-961X", "clpid": "Readhead-A-C-S" } ], "thesis_committee": [ { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Readhead", "given_name": "Anthony C. S.", "orcid": "0000-0001-9152-961X", "clpid": "Readhead-A-C-S" }, { "family_name": "Kulkarni", "given_name": "Shrinivas R.", "orcid": "0000-0001-5390-8563", "clpid": "Kulkarni-S-R" }, { "family_name": "Hirata", "given_name": "Christopher M.", "orcid": "0000-0002-2951-4932", "clpid": "Hirata-C-M" }, { "family_name": "Djorgovski", "given_name": "George", "orcid": "0000-0002-0603-3087", "clpid": "Djorgovski-G" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "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.
", "doi": "10.7907/ZX5X-V114", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:7591", "collection": "thesis", "collection_id": "7591", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04082013-194357946", "primary_object_url": { "basename": "tajones_thesis.pdf", "content": "final", "filesize": 6609058, "license": "other", "mime_type": "application/pdf", "url": "/7591/1/tajones_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Detailed Properties of High Redshift Galaxies", "author": [ { "family_name": "Jones", "given_name": "Tucker A.", "clpid": "Jones-Tucker-A" } ], "thesis_advisor": [ { "family_name": "Ellis", "given_name": "Richard S.", "clpid": "Ellis-R-S" } ], "thesis_committee": [ { "family_name": "Hirata", "given_name": "Christopher M.", "orcid": "0000-0002-2951-4932", "clpid": "Hirata-C-M" }, { "family_name": "Ellis", "given_name": "Richard S.", "clpid": "Ellis-R-S" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Steidel", "given_name": "Charles C.", "orcid": "0000-0002-4834-7260", "clpid": "Steidel-C-C" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Galaxies evolve throughout the history of the universe from the first star-forming sources, through gas-rich asymmetric structures with rapid star formation rates, to the massive symmetrical stellar systems observed at the present day. Determining the physical processes which drive galaxy formation and evolution is one of the most important questions in observational astrophysics. This thesis presents four projects aimed at improving our understanding of galaxy evolution from detailed measurements of star forming galaxies at high redshift.
\r\n\r\nWe use resolved spectroscopy of gravitationally lensed z \u2243 2 - 3 star forming galaxies to measure their kinematic and star formation properties. The combination of lensing with adaptive optics yields physical resolution of \u2243 100 pc, sufficient to resolve giant Hii regions. We find that ~ 70 % of galaxies in our sample display ordered rotation with high local velocity dispersion indicating turbulent thick disks. The rotating galaxies are gravitationally unstable and are expected to fragment into giant clumps. The size and dynamical mass of giant Hii regions are in agreement with predictions for such clumps indicating that gravitational instability drives the rapid star formation. The remainder of our sample is comprised of ongoing major mergers. Merging galaxies display similar star formation rate, morphology, and local velocity dispersion as isolated sources, but their velocity fields are more chaotic with no coherent rotation.
\r\n\r\nWe measure resolved metallicity in four lensed galaxies at z = 2.0 \u2212 2.4 from optical emission line diagnostics. Three rotating galaxies display radial gradients with higher metallicity at smaller radii, while the fourth is undergoing a merger and has an inverted gradient with lower metallicity at the center. Strong gradients in the rotating galaxies indicate that they are growing inside-out with star formation fueled by accretion of metal-poor gas at large radii. By comparing measured gradients with an appropriate comparison sample at z = 0, we demonstrate that metallicity gradients in isolated galaxies must flatten at later times. The amount of size growth inferred by the gradients is in rough agreement with direct measurements of massive galaxies. We develop a chemical evolution model to interpret these data and conclude that metallicity gradients are established by a gradient in the outflow mass loading factor, combined with radial inflow of metal-enriched gas.
\r\n\r\nWe present the first rest-frame optical spectroscopic survey of a large sample of low-luminosity galaxies at high redshift (L < L*, 1.5 < z < 3.5). This population dominates the star formation density of the universe at high redshifts, yet such galaxies are normally too faint to be studied spectroscopically. We take advantage of strong gravitational lensing magnification to compile observations for a sample of 29 galaxies using modest integration times with the Keck and Palomar telescopes. Balmer emission lines confirm that the sample has a median SFR \u223c 10 M_sun yr^\u22121 and extends to lower SFR than has been probed by other surveys at similar redshift. We derive the metallicity, dust extinction, SFR, ionization parameter, and dynamical mass from the spectroscopic data, providing the first accurate characterization of the star-forming environment in low-luminosity galaxies at high redshift. For the first time, we directly test the proposal that the relation between galaxy stellar mass, star formation rate, and gas phase metallicity does not evolve. We find lower gas phase metallicity in the high redshift galaxies than in local sources with equivalent stellar mass and star formation rate, arguing against a time-invariant relation. While our result is preliminary and may be biased by measurement errors, this represents an important first measurement that will be further constrained by ongoing analysis of the full data set and by future observations.
\r\n\r\nWe present a study of composite rest-frame ultraviolet spectra of Lyman break galaxies at z = 4 and discuss implications for the distribution of neutral outflowing gas in the circumgalactic medium. In general we find similar spectroscopic trends to those found at z = 3 by earlier surveys. In particular, absorption lines which trace neutral gas are weaker in less evolved galaxies with lower stellar masses, smaller radii, lower luminosity, less dust, and stronger Ly\u03b1 emission. Typical galaxies are thus expected to have stronger Ly\u03b1 emission and weaker low-ionization absorption at earlier times, and we indeed find somewhat weaker low-ionization absorption at higher redshifts. In conjunction with earlier results, we argue that the reduced low-ionization absorption is likely caused by lower covering fraction and/or velocity range of outflowing neutral gas at earlier epochs. This result has important implications for the hypothesis that early galaxies were responsible for cosmic reionization. We additionally show that fine structure emission lines are sensitive to the spatial extent of neutral gas, and demonstrate that neutral gas is concentrated at smaller galactocentric radii in higher redshift galaxies.
\r\n\r\nThe results of this thesis present a coherent picture of galaxy evolution at high redshifts 2 \u2272 z \u2272 4. Roughly 1/3 of massive star forming galaxies at this period are undergoing major mergers, while the rest are growing inside-out with star formation occurring in gravitationally unstable thick disks. Star formation, stellar mass, and metallicity are limited by outflows which create a circumgalactic medium of metal-enriched material. We conclude by describing some remaining open questions and prospects for improving our understanding of galaxy evolution with future observations of gravitationally lensed galaxies.
", "doi": "10.7907/XB2C-1B49", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:7591", "collection": "thesis", "collection_id": "7591", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04082013-194357946", "primary_object_url": { "basename": "tajones_thesis.pdf", "content": "final", "filesize": 6609058, "license": "other", "mime_type": "application/pdf", "url": "/7591/1/tajones_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Detailed Properties of High Redshift Galaxies", "author": [ { "family_name": "Jones", "given_name": "Tucker A.", "clpid": "Jones-Tucker-A" } ], "thesis_advisor": [ { "family_name": "Ellis", "given_name": "Richard S.", "clpid": "Ellis-R-S" } ], "thesis_committee": [ { "family_name": "Hirata", "given_name": "Christopher M.", "orcid": "0000-0002-2951-4932", "clpid": "Hirata-C-M" }, { "family_name": "Ellis", "given_name": "Richard S.", "clpid": "Ellis-R-S" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Steidel", "given_name": "Charles C.", "orcid": "0000-0002-4834-7260", "clpid": "Steidel-C-C" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Galaxies evolve throughout the history of the universe from the first star-forming sources, through gas-rich asymmetric structures with rapid star formation rates, to the massive symmetrical stellar systems observed at the present day. Determining the physical processes which drive galaxy formation and evolution is one of the most important questions in observational astrophysics. This thesis presents four projects aimed at improving our understanding of galaxy evolution from detailed measurements of star forming galaxies at high redshift.
\r\n\r\nWe use resolved spectroscopy of gravitationally lensed z \u2243 2 - 3 star forming galaxies to measure their kinematic and star formation properties. The combination of lensing with adaptive optics yields physical resolution of \u2243 100 pc, sufficient to resolve giant Hii regions. We find that ~ 70 % of galaxies in our sample display ordered rotation with high local velocity dispersion indicating turbulent thick disks. The rotating galaxies are gravitationally unstable and are expected to fragment into giant clumps. The size and dynamical mass of giant Hii regions are in agreement with predictions for such clumps indicating that gravitational instability drives the rapid star formation. The remainder of our sample is comprised of ongoing major mergers. Merging galaxies display similar star formation rate, morphology, and local velocity dispersion as isolated sources, but their velocity fields are more chaotic with no coherent rotation.
\r\n\r\nWe measure resolved metallicity in four lensed galaxies at z = 2.0 \u2212 2.4 from optical emission line diagnostics. Three rotating galaxies display radial gradients with higher metallicity at smaller radii, while the fourth is undergoing a merger and has an inverted gradient with lower metallicity at the center. Strong gradients in the rotating galaxies indicate that they are growing inside-out with star formation fueled by accretion of metal-poor gas at large radii. By comparing measured gradients with an appropriate comparison sample at z = 0, we demonstrate that metallicity gradients in isolated galaxies must flatten at later times. The amount of size growth inferred by the gradients is in rough agreement with direct measurements of massive galaxies. We develop a chemical evolution model to interpret these data and conclude that metallicity gradients are established by a gradient in the outflow mass loading factor, combined with radial inflow of metal-enriched gas.
\r\n\r\nWe present the first rest-frame optical spectroscopic survey of a large sample of low-luminosity galaxies at high redshift (L < L*, 1.5 < z < 3.5). This population dominates the star formation density of the universe at high redshifts, yet such galaxies are normally too faint to be studied spectroscopically. We take advantage of strong gravitational lensing magnification to compile observations for a sample of 29 galaxies using modest integration times with the Keck and Palomar telescopes. Balmer emission lines confirm that the sample has a median SFR \u223c 10 M_sun yr^\u22121 and extends to lower SFR than has been probed by other surveys at similar redshift. We derive the metallicity, dust extinction, SFR, ionization parameter, and dynamical mass from the spectroscopic data, providing the first accurate characterization of the star-forming environment in low-luminosity galaxies at high redshift. For the first time, we directly test the proposal that the relation between galaxy stellar mass, star formation rate, and gas phase metallicity does not evolve. We find lower gas phase metallicity in the high redshift galaxies than in local sources with equivalent stellar mass and star formation rate, arguing against a time-invariant relation. While our result is preliminary and may be biased by measurement errors, this represents an important first measurement that will be further constrained by ongoing analysis of the full data set and by future observations.
\r\n\r\nWe present a study of composite rest-frame ultraviolet spectra of Lyman break galaxies at z = 4 and discuss implications for the distribution of neutral outflowing gas in the circumgalactic medium. In general we find similar spectroscopic trends to those found at z = 3 by earlier surveys. In particular, absorption lines which trace neutral gas are weaker in less evolved galaxies with lower stellar masses, smaller radii, lower luminosity, less dust, and stronger Ly\u03b1 emission. Typical galaxies are thus expected to have stronger Ly\u03b1 emission and weaker low-ionization absorption at earlier times, and we indeed find somewhat weaker low-ionization absorption at higher redshifts. In conjunction with earlier results, we argue that the reduced low-ionization absorption is likely caused by lower covering fraction and/or velocity range of outflowing neutral gas at earlier epochs. This result has important implications for the hypothesis that early galaxies were responsible for cosmic reionization. We additionally show that fine structure emission lines are sensitive to the spatial extent of neutral gas, and demonstrate that neutral gas is concentrated at smaller galactocentric radii in higher redshift galaxies.
\r\n\r\nThe results of this thesis present a coherent picture of galaxy evolution at high redshifts 2 \u2272 z \u2272 4. Roughly 1/3 of massive star forming galaxies at this period are undergoing major mergers, while the rest are growing inside-out with star formation occurring in gravitationally unstable thick disks. Star formation, stellar mass, and metallicity are limited by outflows which create a circumgalactic medium of metal-enriched material. We conclude by describing some remaining open questions and prospects for improving our understanding of galaxy evolution with future observations of gravitationally lensed galaxies.
", "doi": "10.7907/XB2C-1B49", "publication_date": "2013", "thesis_type": "phd", "thesis_year": "2013" }, { "id": "thesis:7110", "collection": "thesis", "collection_id": "7110", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05312012-150403422", "primary_object_url": { "basename": "Bhalerao-V-B-thesis.pdf", "content": "final", "filesize": 4907106, "license": "other", "mime_type": "application/pdf", "url": "/7110/1/Bhalerao-V-B-thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Neutron Stars and NuSTAR: A Systematic Survey of Neutron Star Masses in High Mass X-ray Binaries & Characterization of CdZnTe Detectors for NuSTAR", "author": [ { "family_name": "Bhalerao", "given_name": "Varun B.", "orcid": "0000-0002-6112-7609", "clpid": "Bhalerao-Varun-B" } ], "thesis_advisor": [ { "family_name": "Harrison", "given_name": "Fiona A.", "clpid": "Harrison-F-A" }, { "family_name": "Kulkarni", "given_name": "Shrinivas R.", "clpid": "Kulkarni-S-R" } ], "thesis_committee": [ { "family_name": "Phinney", "given_name": "E. Sterl", "clpid": "Phinney-E-S" }, { "family_name": "Cohen", "given_name": "Judith G.", "clpid": "Cohen-J-G" }, { "family_name": "Martin", "given_name": "D. Christopher", "clpid": "Martin-D-Christopher" }, { "family_name": "Harrison", "given_name": "Fiona A.", "clpid": "Harrison-F-A" }, { "family_name": "Kulkarni", "given_name": "Shrinivas R.", "clpid": "Kulkarni-S-R" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "My thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy.
\r\n\r\nThe Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here \u2014 from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results.
\r\n\r\nNeutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of \"nature\" and \"nurture\" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses among all classes of neutron star binaries. Intrigued by this diversity \u2014 which points to diverse birth masses \u2014 we undertook a systematic survey to measure the masses of neutron stars in nine high-mass X-ray binaries. In this thesis, I present results from this ongoing project.
\r\n\r\nWhile neutron stars formed the primary focus of my work, I also explored other topics in compact objects. Appendix A describes the discovery and complete characterization of a 1RXS J173006.4+033813, a polar cataclysmic variable. Appendix B describes the discovery of a diamond planet orbiting a millisecond pulsar, and our search for its optical counterpart.
", "doi": "10.7907/CVT1-VR08", "publication_date": "2012", "thesis_type": "phd", "thesis_year": "2012" }, { "id": "thesis:3227", "collection": "thesis", "collection_id": "3227", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08252009-233632", "primary_object_url": { "basename": "kraus_thesis.pdf", "content": "final", "filesize": 6729132, "license": "other", "mime_type": "application/pdf", "url": "/3227/1/kraus_thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Multiple Star Formation", "author": [ { "family_name": "Kraus", "given_name": "Adam L.", "clpid": "Kraus-Adam-L" } ], "thesis_advisor": [ { "family_name": "Hillenbrand", "given_name": "Lynne A.", "clpid": "Hillenbrand-L-A" } ], "thesis_committee": [ { "family_name": "Brown", "given_name": "Michael E.", "orcid": "0000-0002-8255-0545", "clpid": "Brown-M-E" }, { "family_name": "Phinney", "given_name": "E. Sterl", "orcid": "0000-0002-9656-4032", "clpid": "Phinney-E-S" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Hillenbrand", "given_name": "Lynne A.", "clpid": "Hillenbrand-L-A" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "In this thesis, I present a study of the formation and evolution of stars, particularly multiple stellar systems. Binary stars provide a key constraint on star formation because any successful model should reproduce the mass-dependent frequency, distribution of separations, and distribution of mass ratios. I have pursued a number of surveys for different ranges of parameter space, all yielding one overarching conclusion: binary formation is fundamentally tied to mass. Solar-mass stars have a high primordial binary frequency (50%--75%) and a wide range of separations (extending to >10,000 AU), but as the system mass decreases, the frequency and separation distribution also decrease. For brown dwarfs, binaries are rare (~10%--15%) and have separations of <5 AU. Inside of this outer separation cutoff, the separation distribution appears to be log-flat for solar-mass stars, and perhaps for lower-mass systems. Solar-mass binary systems appear to have a flat mass ratio distribution, but for primary masses <0.3 Msun, the distribution becomes increasingly biased toward similar-mass companions.
\r\n\r\nMy results also constrain the binary formation timescale and the postformation evolutionary processes that sculpt binary populations. The dynamical interaction timescale in sparse associations like Taurus and Upper Sco is far longer than their ages, which suggests that those populations are dynamically pristine. However, binary systems in denser clusters undergo significant dynamical processing that strips outer binary companions; the difference in wide binary properties between my sample and the field is explained by the composite origin of the field population. I also have placed the individual components of young binary systems on the HR diagram in order to infer their coevality. In Taurus, binary systems are significantly more coeval (\u0394\u03c4~0.5 Myr) than the association as a whole (\u0394\u03c4~3--5 Myr).
\r\n\r\nFinally, my survey of young very-low-mass stars and brown dwarfs found no planetary-mass companions like the prototypical system 2M1207A+b. Modeling the population as either \"super-Planets\" or \"failed binaries\" indicates that the total frequency of companions with masses >1 MJup is <1%--2%. My survey of young solar-mass stars found no brown dwarf companions; evidence in favor of the brown dwarf desert is marginal, but my results do not exclude its existence.
\r\n", "doi": "10.7907/N0KT-QH17", "publication_date": "2010", "thesis_type": "phd", "thesis_year": "2010" }, { "id": "thesis:3140", "collection": "thesis", "collection_id": "3140", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08152008-140704", "primary_object_url": { "basename": "PBCameron_thesis.pdf", "content": "final", "filesize": 3150386, "license": "other", "mime_type": "application/pdf", "url": "/3140/1/PBCameron_thesis.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Formation and Evolution of Neutron Stars: Astrometry, Timing, and Transients", "author": [ { "family_name": "Cameron", "given_name": "Patrick Brian", "clpid": "Cameron-Patrick-Brian" } ], "thesis_advisor": [ { "family_name": "Kulkarni", "given_name": "Shrinivas R.", "clpid": "Kulkarni-S-R" } ], "thesis_committee": [ { "family_name": "Phinney", "given_name": "E. Sterl", "clpid": "Phinney-E-S" }, { "family_name": "Martin", "given_name": "D. Christopher", "clpid": "Martin-D-Christopher" }, { "family_name": "Cohen", "given_name": "Judith G.", "clpid": "Cohen-J-G" }, { "family_name": "Dekany", "given_name": "Richard G.", "clpid": "Dekany-R-G" }, { "family_name": "Kulkarni", "given_name": "Shrinivas R.", "clpid": "Kulkarni-S-R" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "In order to address open questions regarding the death of massive stars and the evolution of the stellar fossils left behind, we use techniques spanning the electromagnetic spectrum to study the youngest and oldest neutron stars. We begin by exploring and developing a new technique --- ground-based astrometry with adaptive optics. This technology is relatively new to astronomy, and has incredible potential for tracking the motions of stars. We enumerate experimental design consideration for mitigating systematic errors and present an optimal estimation algorithm capable of delivering unprecedented astrometric precision and accuracy from the ground. We verify the performance of our technique using experimental data, and discuss the astrometric potential of adaptive optics on large aperture telescopes. We then apply our knowledge to track the motions of magnetars. These objects harbor ultra-strong magnetic fields and give rise to the most intense high-energy transients in the sky. The proper motion survey presented here is the first of its kind, and is capable of directly addressing the open questions regarding their origin and evolution in a model independent fashion. We also present radio studies of the aftermath of the brightest magnetar flare ever recorded. Finally, we shift to probing the emission mechanism of the oldest neutron stars, millisecond pulsars in globular clusters, that are revived at the end of their by lives their binary companions.\r\n", "doi": "10.7907/HTW7-8X31", "publication_date": "2009", "thesis_type": "phd", "thesis_year": "2009" }, { "id": "thesis:3448", "collection": "thesis", "collection_id": "3448", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09102008-170617", "primary_object_url": { "basename": "Thesis.pdf", "content": "final", "filesize": 1897034, "license": "other", "mime_type": "application/pdf", "url": "/3448/9/Thesis.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Luminous, the Massive and the Dusty: A Near- to Mid-Infrared Spectroscopic Study of Submillimeter Galaxies", "author": [ { "family_name": "Men\u00e9ndez-Delmestre", "given_name": "Kar\u00edn", "orcid": "0000-0003-3153-5123", "clpid": "Men\u00e9ndez-Delmestre-Kar\u00edn" } ], "thesis_advisor": [ { "family_name": "Blain", "given_name": "Andrew W.", "clpid": "Blain-A-W" } ], "thesis_committee": [ { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "clpid": "Scoville-N-Z" }, { "family_name": "Benson", "given_name": "Andrew J.", "clpid": "Benson-A-J" }, { "family_name": "Blain", "given_name": "Andrew W.", "clpid": "Blain-A-W" }, { "family_name": "Cohen", "given_name": "Judith G.", "clpid": "Cohen-J-G" }, { "family_name": "Armus", "given_name": "Lee", "clpid": "Armus-L" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Submillimeter (submm) surveys have uncovered a population of dust-enshrouded ultra-luminous galaxies that are inconspicuous in deep surveys at shorter wavelengths. Inferred to have high star-formation rates (up to more than 1000 Msun/yr), submm-selected galaxies (SMGs) contribute significantly to the global star-formation rate density at z~2-3 and are thus critical players in building up stars in galaxies. Many SMGs have been shown to display X-ray, optical and near-infrared (IR) signatures of active galactic nuclei (AGN), prompting the question: how significant is the AGN contribution to their total luminosity? Central to understanding SMGs is the study of the nature of their power source, their internal dynamics, their SFRs and their masses. We study mid-IR and near-IR spectra of SMGs to investigate these aspects.
\r\n\r\nWe have obtained the largest sample of 24 SMGs to date with the mid-IR Spitzer Infrared Spectrograph (IRS) at z ~ 0.65 - 3.2. Broad PAH emission features -- typically associated to intense star-formation -- are almost ubiquitous in the sample and the composite spectrum is well fit by a combination of a starburst component with an additional power law representing less than a 35% AGN contribution to the bolometric luminosity. We find weak silicate absorption in contrast to local ultra-luminous IR galaxies (ULIRGs), suggesting that the mid-IR visible star formation in SMGs occurs in a more extended component.
\r\n\r\nWe also study the near-IR emission of SMGs with the OH-Suppressing Infrared Imaging Spectrograph (OSIRIS), together with the Keck Laser-Guide Star Adaptive Optics system, to investigate the distribution and dynamics of the ionized gas. The two-dimensional insight of these observations allow us to distinguish and quantify the compact AGN emission, which allows us to refine estimates of dynamical masses, SFRs and gas masses for the population. With a spatially-resolved spectroscopic insight into the kpc-scale structure of these galaxies, we find that the H-alpha emission in SMGs extends over scales ~4-17 kpc, setting SMGs apart from local ULIRGs, where intense emission is confined to the central 1 kpc.
\r\n", "doi": "10.7907/J1R4-5F20", "publication_date": "2009", "thesis_type": "phd", "thesis_year": "2009" }, { "id": "thesis:3526", "collection": "thesis", "collection_id": "3526", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09132007-122424", "primary_object_url": { "basename": "SuyuThesisNewStyle.pdf", "content": "final", "filesize": 7743174, "license": "other", "mime_type": "application/pdf", "url": "/3526/1/SuyuThesisNewStyle.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Dissecting the Gravitational Lens B1608+656: Implications for the Hubble Constant", "author": [ { "family_name": "Suyu", "given_name": "Sherry Hsuan", "orcid": "0000-0001-5568-6052", "clpid": "Suyu-Sherry-Hsuan" } ], "thesis_advisor": [ { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Thorne", "given_name": "Kip S.", "clpid": "Thorne-K-S" } ], "thesis_committee": [ { "family_name": "Thorne", "given_name": "Kip S.", "clpid": "Thorne-K-S" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Cohen", "given_name": "Judith G.", "clpid": "Cohen-J-G" }, { "family_name": "Kamionkowski", "given_name": "Marc P.", "clpid": "Kamionkowski-M-P" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Strong gravitational lens systems provide a tool for probing galaxy mass distributions (independent of their light profiles) and for measuring cosmological parameters. In a strong lens system, the background source intensity distribution is multiply imaged. If the source intensity is time varying, then the multiple images of the variable source are delayed in time relative to each other due to the different light travel time along the multiple light paths. One can use lens systems to measure the Hubble constant by obtaining the relative time delays between the multiple images and modeling the lens potential. B1608+656 is a quadruply imaged gravitational lens system with a spatially extended source intensity distribution and two interacting galaxy lenses. This system is unique in that the three relative time delays between the four images were measured accurately with errors of only a few percent, and it thus provides an opportunity to measure the Hubble constant with high precision. The extended source intensity distribution in B1608+656 provides additional constraints on the lens potential, though simultaneous determination of the source intensity and lens potential distribution is needed. The presence of dust and interacting galaxy lenses further complicate this system. We present a comprehensive analysis in a Bayesian framework that takes into account the extended source intensity distribution, interacting galaxy lenses, and the presence of dust for reconstructing the lens potential. Using the deep HST ACS observations on B1608+656, the resulting statistical uncertainty on H_0 associated with the lens modeling is limited by the uncertainty in the best time delay measurement (~3%). The dominant systematic error on H_0 is due to the effects of the environment on B1608+656 (mass-sheet degeneracy). By using the measured velocity dispersion of the lens galaxies and considering the mass structures along the line of sight to B1608+656, we place constraints on the external convergence associated with galaxy groups and mass structure along the line of sight. The resulting Hubble constant from B1608+656 is H_0 = 72 \u00b1 2 (stat.) \u00b1 4 (syst.) km s^-1 Mpc^-1.\r\n", "doi": "10.7907/MQS2-Y860", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:1825", "collection": "thesis", "collection_id": "1825", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05152008-141502", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 3493601, "license": "other", "mime_type": "application/pdf", "url": "/1825/1/thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Young, Massive Star Clusters in the Antennae", "author": [ { "family_name": "Christopher", "given_name": "Micol Huw", "clpid": "Christopher-Micol-Huw" } ], "thesis_advisor": [ { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" } ], "thesis_committee": [ { "family_name": "Hillenbrand", "given_name": "Lynne A.", "clpid": "Hillenbrand-L-A" }, { "family_name": "Schweizer", "given_name": "Francois", "clpid": "Schweizer-F" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" }, { "family_name": "Ellis", "given_name": "Richard S.", "clpid": "Ellis-R-S" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "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", "doi": "10.7907/QP4P-SD67", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:1825", "collection": "thesis", "collection_id": "1825", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05152008-141502", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 3493601, "license": "other", "mime_type": "application/pdf", "url": "/1825/1/thesis.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Young, Massive Star Clusters in the Antennae", "author": [ { "family_name": "Christopher", "given_name": "Micol Huw", "clpid": "Christopher-Micol-Huw" } ], "thesis_advisor": [ { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" } ], "thesis_committee": [ { "family_name": "Hillenbrand", "given_name": "Lynne A.", "clpid": "Hillenbrand-L-A" }, { "family_name": "Schweizer", "given_name": "Francois", "clpid": "Schweizer-F" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" }, { "family_name": "Ellis", "given_name": "Richard S.", "clpid": "Ellis-R-S" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "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", "doi": "10.7907/QP4P-SD67", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:3090", "collection": "thesis", "collection_id": "3090", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08102007-161741", "primary_object_url": { "basename": "fullthesis.pdf", "content": "final", "filesize": 42720980, "license": "other", "mime_type": "application/pdf", "url": "/3090/13/fullthesis.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "1-10 Myr-Old Low Mass Stars and Brown Dwarfs in Nearby Star Forming Regions", "author": [ { "family_name": "Slesnick", "given_name": "Catherine Louise", "clpid": "Slesnick-Catherine-Louise" } ], "thesis_advisor": [ { "family_name": "Hillenbrand", "given_name": "Lynne A.", "clpid": "Hillenbrand-L-A" } ], "thesis_committee": [ { "family_name": "Brown", "given_name": "Michael E.", "orcid": "0000-0002-8255-0545", "clpid": "Brown-M-E" }, { "family_name": "Sargent", "given_name": "Anneila Isabel", "orcid": "0000-0002-4633-5098", "clpid": "Sargent-A-I" }, { "family_name": "Carpenter", "given_name": "John M.", "orcid": "0000-0003-2251-0602", "clpid": "Carpenter-J-M" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Hillenbrand", "given_name": "Lynne A.", "clpid": "Hillenbrand-L-A" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "My thesis research has focused primarily on identifying and characterizing pre-main sequence stars in nearby star-forming regions. To this end, I carried out wide-field (~150-250 deg\u00b2) optical photometric and spectroscopic surveys in and near the star forming regions of Taurus and Upper Scorpius.
\r\n\r\nIn Taurus, the aim of my optical photometric/spectroscopic survey was specifically to probe for a population of intermediate-age pre-main sequence stars outside of the young subclusters that are known to contain most of the young Taurus population. From this work I found tens of young (~1-3 Myr) and intermediate-age (~5-10 Myr) stars both near the known Taurus population and to the east, but relatively few pre-main sequence stars of any age to the west. I argued that the new pre-main sequence stars identified far from Taurus can not have originated from the vicinity of the 1-2 Myr-old subclusters and I proposed instead that they comprise a new, previously undiscovered region of recent star formation.
\r\n\r\nIn USco, the aim of my optical photometric/spectroscopic survey was to probe beyond previously explored regions to identify large numbers of 5 Myr-old low mass stars. From the spectroscopic data I have discovered 145 low mass members of USco. Using Monte Carlo simulations I showed that, taking into account known observational errors, the observed age dispersion for the low mass population in USco is consistent with all stars forming in a single burst ~5 Myr ago. I also derived the first spectroscopic mass function for USco that extends into the substellar regime and compared results to similar mass functions derived for stars in four other young clusters and associations.
", "doi": "10.7907/D7XM-E815", "publication_date": "2008", "thesis_type": "phd", "thesis_year": "2008" }, { "id": "thesis:1971", "collection": "thesis", "collection_id": "1971", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05232005-155338", "primary_object_url": { "basename": "main.pdf", "content": "final", "filesize": 2036830, "license": "other", "mime_type": "application/pdf", "url": "/1971/2/main.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Adventures in Theoretical Astrophysics", "author": [ { "family_name": "Farmer", "given_name": "Alison Jane", "clpid": "Farmer-Alison-Jane" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Cohen", "given_name": "Judith G.", "clpid": "Cohen-J-G" }, { "family_name": "Kamionkowski", "given_name": "Marc P.", "clpid": "Kamionkowski-M-P" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Sari", "given_name": "Re'em", "clpid": "Sari-R" }, { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "This thesis is a tour of topics in theoretical astrophysics, unified by their diversity and their pursuit of physical understanding of astrophysical phenomena.
\r\n\r\nIn the first chapter, we raise the possibility of the detection of white dwarfs in transit surveys for extrasolar Earths, and discuss the peculiarities of detecting these more massive objects.
\r\n\r\nA population synthesis calculation of the gravitational wave background from extragalactic binary stars is then presented. In this study, we establish a firm understanding of the uncertainties in such a calculation and provide a valuable reference for planning the Laser Interferometer Space Antenna mission.
\r\n\r\nThe long-established problem of cosmic ray confinement to the Galaxy is addressed in another chapter. We introduce a new wave damping mechanism, due to the presence of background turbulence, that prevents the confinement of cosmic rays by the resonant streaming instability.
\r\n\r\nWe also investigate the spokes in Saturn's B ring, an electrodynamic mystery that is being illuminated by new data sent back from the Cassini spacecraft. In particular, we present assessments of the presence of charged dust near the rings, and the size of currents and electric fields in the ring system. We make inferences from the Cassini discovery of oxygen ions above the rings. In addition, the previous leading theory for spoke formation is demonstrated to be unphysical.
\r\n\r\nIn the final chapter, we explain the wayward motions of Prometheus and Pandora, two small moons of Saturn. Previously found to be chaotic as a result of mutual interactions, we account for their behavior by analogy with a parametric pendulum. We caution that this behavior may soon enter a new regime.
", "doi": "10.7907/JJKJ-J144", "publication_date": "2005", "thesis_type": "phd", "thesis_year": "2005" }, { "id": "thesis:3596", "collection": "thesis", "collection_id": "3596", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09172008-111737", "primary_object_url": { "basename": "Behr_bb_2000.pdf", "content": "final", "filesize": 5366317, "license": "other", "mime_type": "application/pdf", "url": "/3596/1/Behr_bb_2000.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "A New Spin on Horizontal-Branch Stars: Anomalous Abundances and Rapid Rotation Rates", "author": [ { "family_name": "Behr", "given_name": "Bradford B.", "clpid": "Behr-Bradford-B" } ], "thesis_advisor": [ { "family_name": "McCarthy", "given_name": "James K.", "clpid": "McCarthy-James-K" } ], "thesis_committee": [ { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Djorgovski", "given_name": "George", "orcid": "0000-0002-0603-3087", "clpid": "Djorgovski-G" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "McCarthy", "given_name": "James K.", "clpid": "McCarthy-James-K" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "High-resolution spectroscopy of blue horizontal-branch stars in metal-poor globular clusters reveals remarkable differences in photospheric composition and rotation rate between cooler and hotter stars. For the cooler stars (Teff < 11000 K), the derived abundances are in good agreement with the canonical cluster metallicities, and we confirm the range of v sin i rotation velocities, some as high as 40 km s-1, previously reported in the literature. In the hotter stars, however, metals are enhanced by factors of 100 or more, and helium is depleted by as much as two orders of magnitude. In addition, the hot stars are almost exclusively slow rotators, with v sin i < 8 km s-1. The anomalous abundances are due to atomic diffusion mechanisms \u2014 gravitational settling of helium, and radiative levitation of metals - in the stable, non-convective atmospheres of these hot stars. The enhanced metal content in the stellar photospheres can alter the emergent spectral energy distributions, creating the photometric \"gaps\" observed in the clusters' color-magnitude diagrams. We discuss the connections between rotation and the diffusion mechanisms, and explore potential implications regarding the internal structure and evolution of these stars.", "doi": "10.7907/rdxg-qg24", "publication_date": "2000", "thesis_type": "phd", "thesis_year": "2000" }, { "id": "thesis:3736", "collection": "thesis", "collection_id": "3736", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09232008-142919", "primary_object_url": { "basename": "Wu_y_1998.pdf", "content": "final", "filesize": 8367380, "license": "other", "mime_type": "application/pdf", "url": "/3736/1/Wu_y_1998.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Excitation and Saturation of White Dwarf Pulsation", "author": [ { "family_name": "Wu", "given_name": "Yanqin", "orcid": "0000-0003-0511-0893", "clpid": "Wu-Yanqin" } ], "thesis_advisor": [ { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "McCarthy", "given_name": "James K.", "clpid": "McCarthy-James-K" }, { "family_name": "Phinney", "given_name": "E. Sterl", "orcid": "0000-0002-9656-4032", "clpid": "Phinney-E-S" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Variable hydrogen white dwarfs (DAV) pulsate in a number of low-order gravity-modes with periods from 100 s to 1200 s and amplitudes no larger than a few percent. We answer two questions in this thesis: the driving for these pulsations, and the saturation of their amplitudes.
\r\n\r\nThe surface convection zone in these stars, which adjusts its entropy level instantaneously during the pulsation, can drive the observed modes. This mechanism (called 'convective driving') was discovered by Brickhill but has been largely neglected so far. We find that modes with periods shorter than the thermal adjustment time of the convection zone can become overstable, but those with very short periods are hardly visible at the surface. As the star cools and the convection zone deepens, longer period modes can be excited. The driving rates increase sharply with period. We relate these to the time-scale of mode variability. We include complications arising from nonadiabaticity in the radiative interior and turbulent damping at the convective-radiative boundary. The former limits the driving and damping rates for strongly nonadiabatic modes, and relates the phase and amplitude of surface horizontal velocity in a gravity-mode to those of its flux variation. The turbulent damping results from the horizontal velocity shear below the convection zone, inside which there is little velocity shear and negligible damping. This suppresses the amplitudes of long period modes to below detection. The width of the theoretical DAV instability strip is about 1000 K.
\r\n\r\nThe growth of an overstable mode can be saturated by parametric instability, where energy transfers resonantly into two damped modes of roughly half its frequency. This occurs above a critical amplitude which depends on the 3-mode coupling coefficient and the nonadiabatic damping rates. The critical amplitudes all fall below a few percent, with longer period modes having larger surface amplitudes. Combined with the amplitude limits due to turbulent damping, our estimates compare well with observations. Other types of mode couplings are needed to explain the observed 'mode selection'.
\r\n\r\nFinally, we show that the combination frequencies found in pulsation power spectra are produced by the time-varying convection zone which nonlinearly affects mode visibility.
", "doi": "10.7907/nc60-8v65", "publication_date": "1998", "thesis_type": "phd", "thesis_year": "1998" }, { "id": "thesis:3736", "collection": "thesis", "collection_id": "3736", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09232008-142919", "primary_object_url": { "basename": "Wu_y_1998.pdf", "content": "final", "filesize": 8367380, "license": "other", "mime_type": "application/pdf", "url": "/3736/1/Wu_y_1998.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Excitation and Saturation of White Dwarf Pulsation", "author": [ { "family_name": "Wu", "given_name": "Yanqin", "orcid": "0000-0003-0511-0893", "clpid": "Wu-Yanqin" } ], "thesis_advisor": [ { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "McCarthy", "given_name": "James K.", "clpid": "McCarthy-James-K" }, { "family_name": "Phinney", "given_name": "E. Sterl", "orcid": "0000-0002-9656-4032", "clpid": "Phinney-E-S" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Variable hydrogen white dwarfs (DAV) pulsate in a number of low-order gravity-modes with periods from 100 s to 1200 s and amplitudes no larger than a few percent. We answer two questions in this thesis: the driving for these pulsations, and the saturation of their amplitudes.
\r\n\r\nThe surface convection zone in these stars, which adjusts its entropy level instantaneously during the pulsation, can drive the observed modes. This mechanism (called 'convective driving') was discovered by Brickhill but has been largely neglected so far. We find that modes with periods shorter than the thermal adjustment time of the convection zone can become overstable, but those with very short periods are hardly visible at the surface. As the star cools and the convection zone deepens, longer period modes can be excited. The driving rates increase sharply with period. We relate these to the time-scale of mode variability. We include complications arising from nonadiabaticity in the radiative interior and turbulent damping at the convective-radiative boundary. The former limits the driving and damping rates for strongly nonadiabatic modes, and relates the phase and amplitude of surface horizontal velocity in a gravity-mode to those of its flux variation. The turbulent damping results from the horizontal velocity shear below the convection zone, inside which there is little velocity shear and negligible damping. This suppresses the amplitudes of long period modes to below detection. The width of the theoretical DAV instability strip is about 1000 K.
\r\n\r\nThe growth of an overstable mode can be saturated by parametric instability, where energy transfers resonantly into two damped modes of roughly half its frequency. This occurs above a critical amplitude which depends on the 3-mode coupling coefficient and the nonadiabatic damping rates. The critical amplitudes all fall below a few percent, with longer period modes having larger surface amplitudes. Combined with the amplitude limits due to turbulent damping, our estimates compare well with observations. Other types of mode couplings are needed to explain the observed 'mode selection'.
\r\n\r\nFinally, we show that the combination frequencies found in pulsation power spectra are produced by the time-varying convection zone which nonlinearly affects mode visibility.
", "doi": "10.7907/nc60-8v65", "publication_date": "1998", "thesis_type": "phd", "thesis_year": "1998" }, { "id": "thesis:10969", "collection": "thesis", "collection_id": "10969", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302018-084028309", "primary_object_url": { "basename": "Knop_RA_1997.pdf", "content": "final", "filesize": 63346835, "license": "other", "mime_type": "application/pdf", "url": "/10969/1/Knop_RA_1997.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Spatially Resolved Infrared Spectroscopy of Seyfert Galaxies", "author": [ { "family_name": "Knop", "given_name": "Robert A., Jr.", "clpid": "Knop-Robert-A-Jr" } ], "thesis_advisor": [ { "family_name": "Soifer", "given_name": "B. Thomas", "clpid": "Soifer-B-T" } ], "thesis_committee": [ { "family_name": "Cohen", "given_name": "Judith G.", "clpid": "Cohen-J-G" }, { "family_name": "Phinney", "given_name": "E. Sterl", "clpid": "Phinney-E-S" }, { "family_name": "Phillips", "given_name": "Thomas G.", "clpid": "Phillips-T-G" }, { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "This thesis presents infrared spectroscopy of the circumnuclear regions of 23 Seyfert galaxies. Observations are spectrally resolved with a resolution of \u03bb/\u0394\u03bb ~ 1000 and spatially resolved to ~ 1\", corresponding to ~ 102 pc for the objects in the sample. The instrument used for the observations, the Palomar Near-Infrared Spectrometer, is described, and problems peculiar to reduction of data from it are discussed. The lines observed include Pa\u03b2, Br\u03b3, [FeII] (\u03bb=l.2567\u03bcm), and H2 (\u03bb=2.1213\u03bcm). In nine objects, the coronal line [SIX] (\u03bb=l.2524\u03bcm) is also detected. Spatially resolved line emission is clearly visible in approximately half of the objects observed. The data for five of the objects showing the best spatially resolved infrared line emission are analyzed in detail. These objects include Seyfert 1.5 galaxy NGC 4151 and Seyfert 2 galaxies Mk 1066, NGC 2110, NGC 4388, and Mk 3. The data for the remaining objects is presented in tabular form, and each object is discussed briefly. The data argue that processes associated with the Seyfert nucleus are responsible for the bulk of the observed [FeII] emission. Kinematic and spatial associations can be drawn between features in the [FeII] line profiles and other processes associated with the active nucleus, such as outflows seen in ionized optical emission and radio lobes. Most of the [FeII] appears to emerge from partially ionized regions excited by nuclear x-rays, with an additional contribution from fast shocks. Some of the H2 emission also appears to be associated with the nuclear activity. However, in some cases the H2 emission is observed to have a different spatial distribution from [FeII] and the H+ emission. The H2 emission is probably thermally excited. No significant differences are found between the infrared line emission of Seyfert and Seyfert l.x galaxies.
", "doi": "10.7907/GZ2H-3X10", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:3743", "collection": "thesis", "collection_id": "3743", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09242008-091045", "primary_object_url": { "basename": "Tinney_cg_1993.pdf", "content": "final", "filesize": 10663227, "license": "other", "mime_type": "application/pdf", "url": "/3743/1/Tinney_cg_1993.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The faintest stars", "author": [ { "family_name": "Tinney", "given_name": "Christopher G.", "clpid": "Tinney-C-G" } ], "thesis_advisor": [ { "family_name": "Mould", "given_name": "Jeremy R.", "clpid": "Mould-J-R" }, { "family_name": "Reid", "given_name": "Neill", "clpid": "Reid-N" } ], "thesis_committee": [ { "family_name": "Mould", "given_name": "Jeremy R.", "clpid": "Mould-J-R" }, { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Cohen", "given_name": "Judith G.", "clpid": "Cohen-J-G" }, { "family_name": "Reid", "given_name": "Neill", "clpid": "Reid-N" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "clpid": "Scoville-N-Z" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\n\nWe construct a 270 square degree photometric catalogue from plate material of the UKSRC and POSSII surveys. The procedures used and quality checks applied are described in detail, and should be considered as illustrative for those planning scientific programmes with the forthcoming scans of these surveys.\n\nInfrared JHKLL' photometry and low resolution infrared spectra (\u03bb \u2248 1.0-2.5\u03bcm) for a selection of the latest stars known are presented. The combined photometric and spectral data are used to evaluate bolometric corrections and bolometric magnitudes for late type M-dwarfs almost 2-magnitudes fainter than the faintest previously measured objects. We examine some of the current problems associated with the effective temperature scale for very low mass stars.\n\nFirst results are presented from a CCD trigonometric parallax programme at the Palomar 60\" telescope. We double the number of extremely late M-dwarfs (M[subscript bol] > 13) with directly measured distances. Structure in the main sequences so constructed suggest that the faintest known stars may not be stably supported by nuclear burning. We show that \u03c3(\u03c0) \u2264 0.004\" can be obtained in a few years using standard CCDs on a common-user telescope.\n\nWe present infrared K-band photometry of complete samples of VLM candidates selected by our photographic catalogues, and construct a bolometric luminosity function which extends to M[subscript Bol] = 13.75. We find significant evidence for a luminosity function decreasing towards these luminosities. We also find that our data are consistent with the results of studies based on the Nearby Star sample. We convert our observed LF into the form of a mass function which extends with reasonable statistics to 0.08M[...] \u2014 the H-burning minimum mass. The mass function 'turns over' at \u2248 0.25M[...], goes through a local minimum at \u2248 0.15M[...], and seems to increase again below 0.1M[...] \u2014 none of these features are predicted by any of the current theories of star formation. Lastly, the mass density we observe just above the H-burning minimum mass makes it difficult to envisage brown dwarfs contributing significant quantities of missing mass without invoking either a mass function in this region significantly steeper than that seen for main sequence stars, or an extremely low cut-off mass to the mass function.\n", "doi": "10.7907/0wrn-f607", "publication_date": "1993", "thesis_type": "phd", "thesis_year": "1993" }, { "id": "thesis:2578", "collection": "thesis", "collection_id": "2578", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06132007-132124", "type": "thesis", "title": "A Non-LTE Analysis of a Sample of O Stars Selected from Galactic OB Associations", "author": [ { "family_name": "Budge", "given_name": "Kent Grimmett", "clpid": "Budge-Kent-Grimmett" } ], "thesis_advisor": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "clpid": "Libbrecht-K-G" }, { "family_name": "Boesgaard", "given_name": "Ann Merchant", "clpid": "Boesgaard-A-M" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Mould", "given_name": "Jeremy R.", "clpid": "Mould-J-R" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Boesgaard", "given_name": "Ann Merchant", "clpid": "Boesgaard-A-M" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "The tables of non-LTE line profiles and equivalent widths published by Mihalas and his collaborators [33], [7], [35] have been revised and extended to four different values of the abundance ratio He/H. Bolometric corrections have been calculated for V magnitudes. The theoretical line profiles have been fit to echelle spectrograms of 22 galactic O stars by \u03c7\u00b2 minimization. It is found that the stars with the lowest surface gravities are fitted best by theoretical spectra with unexpectedly high helium abundances (He/H ~ 0.50), while the stars with higher surface gravities are fitted best by theoretical spectra with He/H ~ 0.10, the accepted cosmic ratio. This suggests a systematic failure of conventional non-LTE, plane-parallel models for the more luminous O stars, probably as a result of the neglect of geometrical dilution.
\r\n\r\nThe formula, log He/H = 1.1234-0.4791 log g, gives a good fit to the relation between the apparent helium abundance and log g. Using this relationship, the apparent abundances have been reduced to what are probably true abundances relative to the normal cosmic abundance. It is found that there is no significant difference in the average helium abundances of the associations observed. However, the stars HD 12993, HD 242908, and HD 193595 may be blue stragglers with moderately enhanced helium abundance (He/H ~ 0.19).
\r\n\r\nRelative carbon abundances have been determined empirically by comparison of the CIV 5812\u00c5 and HeII 4542\u00c5 equivalent widths. It is found that the association Cyg 0B2 is overabundant in carbon by ~50%. Likewise, the blue straggler HD 236894 is underabundant in carbon by a factor of two.
\r\n\r\nThe estimated effective temperatures of the sample are compared to the previously accepted calibration of MK spectral types to the effective temperature. Estimates of the radii and masses of the stars in the sample have been calculated from their physical parameters and their absolute visual magnitudes.
", "doi": "10.7907/A24K-G089", "publication_date": "1990", "thesis_type": "phd", "thesis_year": "1990" }, { "id": "thesis:2578", "collection": "thesis", "collection_id": "2578", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06132007-132124", "type": "thesis", "title": "A Non-LTE Analysis of a Sample of O Stars Selected from Galactic OB Associations", "author": [ { "family_name": "Budge", "given_name": "Kent Grimmett", "clpid": "Budge-Kent-Grimmett" } ], "thesis_advisor": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "clpid": "Libbrecht-K-G" }, { "family_name": "Boesgaard", "given_name": "Ann Merchant", "clpid": "Boesgaard-A-M" } ], "thesis_committee": [ { "family_name": "Libbrecht", "given_name": "Kenneth George", "orcid": "0000-0002-8744-3298", "clpid": "Libbrecht-K-G" }, { "family_name": "Mould", "given_name": "Jeremy R.", "clpid": "Mould-J-R" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Boesgaard", "given_name": "Ann Merchant", "clpid": "Boesgaard-A-M" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "The tables of non-LTE line profiles and equivalent widths published by Mihalas and his collaborators [33], [7], [35] have been revised and extended to four different values of the abundance ratio He/H. Bolometric corrections have been calculated for V magnitudes. The theoretical line profiles have been fit to echelle spectrograms of 22 galactic O stars by \u03c7\u00b2 minimization. It is found that the stars with the lowest surface gravities are fitted best by theoretical spectra with unexpectedly high helium abundances (He/H ~ 0.50), while the stars with higher surface gravities are fitted best by theoretical spectra with He/H ~ 0.10, the accepted cosmic ratio. This suggests a systematic failure of conventional non-LTE, plane-parallel models for the more luminous O stars, probably as a result of the neglect of geometrical dilution.
\r\n\r\nThe formula, log He/H = 1.1234-0.4791 log g, gives a good fit to the relation between the apparent helium abundance and log g. Using this relationship, the apparent abundances have been reduced to what are probably true abundances relative to the normal cosmic abundance. It is found that there is no significant difference in the average helium abundances of the associations observed. However, the stars HD 12993, HD 242908, and HD 193595 may be blue stragglers with moderately enhanced helium abundance (He/H ~ 0.19).
\r\n\r\nRelative carbon abundances have been determined empirically by comparison of the CIV 5812\u00c5 and HeII 4542\u00c5 equivalent widths. It is found that the association Cyg 0B2 is overabundant in carbon by ~50%. Likewise, the blue straggler HD 236894 is underabundant in carbon by a factor of two.
\r\n\r\nThe estimated effective temperatures of the sample are compared to the previously accepted calibration of MK spectral types to the effective temperature. Estimates of the radii and masses of the stars in the sample have been calculated from their physical parameters and their absolute visual magnitudes.
", "doi": "10.7907/A24K-G089", "publication_date": "1990", "thesis_type": "phd", "thesis_year": "1990" }, { "id": "thesis:3594", "collection": "thesis", "collection_id": "3594", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09172008-093354", "type": "thesis", "title": "Echelle Spectroscopy of the Central Stars of Planetary Nebulae", "author": [ { "family_name": "McCarthy", "given_name": "James K.", "clpid": "McCarthy-James-K" } ], "thesis_advisor": [ { "family_name": "Mould", "given_name": "Jeremy R.", "orcid": "0000-0003-3820-1740", "clpid": "Mould-J-R" } ], "thesis_committee": [ { "family_name": "Mould", "given_name": "Jeremy R.", "orcid": "0000-0003-3820-1740", "clpid": "Mould-J-R" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Greenstein", "given_name": "Jesse L.", "clpid": "Greenstein-J-L" }, { "family_name": "Oke", "given_name": "J. Beverly", "clpid": "Oke-J-B" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" }, { "family_name": "Shectman", "given_name": "Stephen Alan", "orcid": "0000-0002-8681-6136", "clpid": "Shectman-S-A" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Presented in this work are the results of a spectroscopic study of the central stars of planetary nebulae (CSPN) conducted at high resolution. From detailed comparisons of their photospheric absorption line profiles observed at high signal-to-noise with the NLTE model atmosphere line profiles of Kudritzki, et al., in Munich, West Germany, the photospheric effective temperatures (Teff), surface gravities (g), and helium abundances (y) were derived. Placement of the CSPN in the distance-independent log(g) - log(Teff) diagram allowed central star masses and evolutionary ages to be deduced via comparisons with published evolutionary model calculations. Spectroscopic distances to the CSPN were estimated from the best fit model fluxes, leading to dynamical expansion ages for the surrounding nebulae which were typically much greater than the corresponding CSPN evolutionary ages. Two possible reasons for this timescale disagreement were quantitatively investigated: (1) the nebulae could have experienced a phase of rapid photo-ionization of material ejected while the stars were still on the AGB, or (2) the AGB - CSPN evolutionary transition times could have been increased by small additional amounts of residual envelope material remaining after the superwind mass loss phase.
\r\n\r\nAn important preliminary phase of this project was the design and construction of a CCD echelle spectrograph for the Palomar 1.5 m telescope. The spectrograph was designed to cover the wavelength range 3200 \u00c5 to 7000 \u00c5, utilizing 57 diffracted orders from the echelle grating. Fused quartz prism cross-dispersing elements and an all-transmitting camera lens system contribute to the extremely high throughput of the instrument; the combined telescope and echelle spectrograph efficiency is approximately 20% from above the atmosphere. Details of the echelle spectrograph optical and mechanical designs are presented.
\r\n\r\nThe scientific objectives of the CSPN study with this new instrument required a thorough investigation into the data reduction process for CCD echelle spectra, and a set of Fortran subroutines were written for this purpose as part of the FIGARO data reduction package. The philosophy and algorithms employed in these routines are discussed, and a detailed description of each of the commands is provided in an Appendix for future reference.
\r\n", "doi": "10.7907/jzsq-vr40", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:7454", "collection": "thesis", "collection_id": "7454", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01302013-100511748", "primary_object_url": { "basename": "Summers_me_1985.pdf", "content": "final", "filesize": 18944426, "license": "other", "mime_type": "application/pdf", "url": "/7454/1/Summers_me_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Theoretical Studies of Io's Atmosphere", "author": [ { "family_name": "Summers", "given_name": "Michael Earl", "orcid": "0000-0001-5986-8902", "clpid": "Summers-Michael-Earl" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A range of theoretical models of the compositional structure of Io's dayside atmosphere and ionosphere are developed. The dominant neutral gas, SO2, is provided by sublimation of surface frost. Photochemical processes lead to the build up of O, S, SO, and O2 as minor gasses near Io's surface while O becomes the dominant gas near the exobase. The vertical column density of O2 in all models considered is less than 1014 cm-2. The dayside ionosphere is formed as a result of ionization of neutral species by solar UV radiation. Charge exchange and rearrangement reactions are important for determining the ionic composition of the ionosphere. The dominant ion in the models considered is SO+. A number of charge exchange reactions are identified whose rates need to be better determined in order to refine the present model of the ionosphere. The best matches of the model ionospheres to that observed by the Pioneer 10 radio occultation experiment require atmospheric surface concentrations of SO2 in the range of 2.5 x 109 to 1 x 1011 cm-3, and an exospheric temperature in the range of 960 K to 1230 K. The ratio of the escape fluxes of O to S from the exobase is \u2265 2 in the models considered, while the models which allow surface deposition of minor constituents always have a total sulfur depositional rate greater than 1/2 of the total oxygen depositional rate, thus a surface enrichment of S relative to that predicted by a pure SO2 surface. The depositional rate of this \"excess\" sulfur is in the range 100 m to 1 km thickness per billion years.
\r\n\r\nAtmospheric Na is provided by surface sputtering of SO2 surface frost with Na impurities by MeV type magnetospheric ions. An upward flux of Na2O of S x 107 cm-2 s-1 leads to an escape flux of Na from the exobase of 1 x 107 cm-2 s-1. The chemistry (ion and neutral) of Na species in the atmosphere has only minor effects on the major characteristics of the atmosphere and ionosphere.
\r\n\r\nIt is generally accepted that Io is the source of S, O, Na, and K which, subsequent to ionization, form the constituents of the Io plasma torus. It is shown in chapter II that the escape of S and O from Io can be understood in terms of the photochemistry of a predominantly SO2 atmosphere created by the high vapor pressure of SO2. However, the vapor pressures of Na2S, K2S and other common compounds containing Na and K are negligible at the surface temperature of Io. In chapter III we propose that Na and K escape from Io in two stages. Atoms of Na and K (or molecules containing these atoms) are first sputtered into the atmosphere from the surface by high energy magnetospheric ions. Atmospheric sputtering by low energy corotating ions then removes these constituents (along with others present) out of Io's gravitational control. The estimated injection rates are sufficiently large to maintain the observed Na, K, and O clouds observed around Io.
", "doi": "10.7907/rsm8-qh33", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:7454", "collection": "thesis", "collection_id": "7454", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01302013-100511748", "primary_object_url": { "basename": "Summers_me_1985.pdf", "content": "final", "filesize": 18944426, "license": "other", "mime_type": "application/pdf", "url": "/7454/1/Summers_me_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Theoretical Studies of Io's Atmosphere", "author": [ { "family_name": "Summers", "given_name": "Michael Earl", "orcid": "0000-0001-5986-8902", "clpid": "Summers-Michael-Earl" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "A range of theoretical models of the compositional structure of Io's dayside atmosphere and ionosphere are developed. The dominant neutral gas, SO2, is provided by sublimation of surface frost. Photochemical processes lead to the build up of O, S, SO, and O2 as minor gasses near Io's surface while O becomes the dominant gas near the exobase. The vertical column density of O2 in all models considered is less than 1014 cm-2. The dayside ionosphere is formed as a result of ionization of neutral species by solar UV radiation. Charge exchange and rearrangement reactions are important for determining the ionic composition of the ionosphere. The dominant ion in the models considered is SO+. A number of charge exchange reactions are identified whose rates need to be better determined in order to refine the present model of the ionosphere. The best matches of the model ionospheres to that observed by the Pioneer 10 radio occultation experiment require atmospheric surface concentrations of SO2 in the range of 2.5 x 109 to 1 x 1011 cm-3, and an exospheric temperature in the range of 960 K to 1230 K. The ratio of the escape fluxes of O to S from the exobase is \u2265 2 in the models considered, while the models which allow surface deposition of minor constituents always have a total sulfur depositional rate greater than 1/2 of the total oxygen depositional rate, thus a surface enrichment of S relative to that predicted by a pure SO2 surface. The depositional rate of this \"excess\" sulfur is in the range 100 m to 1 km thickness per billion years.
\r\n\r\nAtmospheric Na is provided by surface sputtering of SO2 surface frost with Na impurities by MeV type magnetospheric ions. An upward flux of Na2O of S x 107 cm-2 s-1 leads to an escape flux of Na from the exobase of 1 x 107 cm-2 s-1. The chemistry (ion and neutral) of Na species in the atmosphere has only minor effects on the major characteristics of the atmosphere and ionosphere.
\r\n\r\nIt is generally accepted that Io is the source of S, O, Na, and K which, subsequent to ionization, form the constituents of the Io plasma torus. It is shown in chapter II that the escape of S and O from Io can be understood in terms of the photochemistry of a predominantly SO2 atmosphere created by the high vapor pressure of SO2. However, the vapor pressures of Na2S, K2S and other common compounds containing Na and K are negligible at the surface temperature of Io. In chapter III we propose that Na and K escape from Io in two stages. Atoms of Na and K (or molecules containing these atoms) are first sputtered into the atmosphere from the surface by high energy magnetospheric ions. Atmospheric sputtering by low energy corotating ions then removes these constituents (along with others present) out of Io's gravitational control. The estimated injection rates are sufficiently large to maintain the observed Na, K, and O clouds observed around Io.
", "doi": "10.7907/rsm8-qh33", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:11856", "collection": "thesis", "collection_id": "11856", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10242019-095223820", "type": "thesis", "title": "Near Infrared Studies of Reflection Nebulae", "author": [ { "family_name": "Sellgren", "given_name": "Kristen", "orcid": "0000-0003-0817-2862", "clpid": "Sellgren-Kristen" } ], "thesis_advisor": [ { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" } ], "thesis_committee": [ { "family_name": "Soifer", "given_name": "B. Thomas", "clpid": "Soifer-B-T" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Houck", "given_name": "James R.", "clpid": "Houck-James-R" }, { "family_name": "Porter", "given_name": "Frank C.", "orcid": "0000-0003-1948-8889", "clpid": "Porter-F-C" }, { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Near infrared studies have been made of the extended emission from, and stellar clusters within, three visual reflection nebulae, NGC 7023, 2023, and 2068. The extended emission from each nebula consists of a smooth continuum from 1.25 to 4.8 \u03bcm, which can be described by a greybody with a color temperature of ~1000 K, and strong emission features at 3.3 and 3.4 \u03bcm. The spectrum is the same in all three sources, and is independent of position over regions 0.4-0.9 pc in diameter within each source. The 2.2 \u03bcm surface brightness distributions in NGC 7023 and 2023 agree well with the distributions of visual reflected light. The continuum emission cannot be explained by free-free emission, reflected light, fluorescent processes, field stars, or thermal emission from grains in equilibrium with the stellar radiation field.
\r\n\r\nA model is proposed in which the extended emission is due to thermal emission from very small grains (radius ~10 \u00c5) which are briefly heated to ~1000 K by absorption of an ultraviolet photon. This model explains the agreement between near infrared and visual surface brightness distributions, and the constancy of the energy distribution with offset from the central stars. The numbers of 10 \u00c5 sized grains required by the observations are in agreement with the numbers expected from an extrapolation of the grain size distribution of Mathis, Rumpl, and Nordsieck (1977) to smaller grain sizes.
\r\n\r\nClusters of young stars found associated with the reflection nebulae NGC 7023, 2023, and 2068 have also been studied at near infrared wavelengths. At least 30-60 % of the stars found at 2.2 \u03bcm are pre-main sequence objects, as indicated by their infrared excesses, hydrogen line emission, or irregular variability. The spatial distributions and observed luminosity functions of these young open clusters are derived, and the inferred mass function and star formation efficiencies are discussed.
", "doi": "10.7907/8dpe-n502", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:11856", "collection": "thesis", "collection_id": "11856", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10242019-095223820", "type": "thesis", "title": "Near Infrared Studies of Reflection Nebulae", "author": [ { "family_name": "Sellgren", "given_name": "Kristen", "orcid": "0000-0003-0817-2862", "clpid": "Sellgren-Kristen" } ], "thesis_advisor": [ { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" } ], "thesis_committee": [ { "family_name": "Soifer", "given_name": "B. Thomas", "clpid": "Soifer-B-T" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Houck", "given_name": "James R.", "clpid": "Houck-James-R" }, { "family_name": "Porter", "given_name": "Frank C.", "orcid": "0000-0003-1948-8889", "clpid": "Porter-F-C" }, { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Near infrared studies have been made of the extended emission from, and stellar clusters within, three visual reflection nebulae, NGC 7023, 2023, and 2068. The extended emission from each nebula consists of a smooth continuum from 1.25 to 4.8 \u03bcm, which can be described by a greybody with a color temperature of ~1000 K, and strong emission features at 3.3 and 3.4 \u03bcm. The spectrum is the same in all three sources, and is independent of position over regions 0.4-0.9 pc in diameter within each source. The 2.2 \u03bcm surface brightness distributions in NGC 7023 and 2023 agree well with the distributions of visual reflected light. The continuum emission cannot be explained by free-free emission, reflected light, fluorescent processes, field stars, or thermal emission from grains in equilibrium with the stellar radiation field.
\r\n\r\nA model is proposed in which the extended emission is due to thermal emission from very small grains (radius ~10 \u00c5) which are briefly heated to ~1000 K by absorption of an ultraviolet photon. This model explains the agreement between near infrared and visual surface brightness distributions, and the constancy of the energy distribution with offset from the central stars. The numbers of 10 \u00c5 sized grains required by the observations are in agreement with the numbers expected from an extrapolation of the grain size distribution of Mathis, Rumpl, and Nordsieck (1977) to smaller grain sizes.
\r\n\r\nClusters of young stars found associated with the reflection nebulae NGC 7023, 2023, and 2068 have also been studied at near infrared wavelengths. At least 30-60 % of the stars found at 2.2 \u03bcm are pre-main sequence objects, as indicated by their infrared excesses, hydrogen line emission, or irregular variability. The spatial distributions and observed luminosity functions of these young open clusters are derived, and the inferred mass function and star formation efficiencies are discussed.
", "doi": "10.7907/8dpe-n502", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" } ]