This thesis is a spectropolarimetric survey of broad absorption line quasi-stellar objects (BAL QSO). We observed 36 BAL QSO at low resolution with the 5 m Hale Telescope at Palomar Observatory and the 10 m Keck Telescopes at the W. M. Keck Observatory.
\r\n\r\nThe continuum, absorption trough, and emission line polarization of BAL QSO were studied in detail, yielding clues about the geometrical structure of gas in the inner regions of quasars. BAL QSO have, on average, higher polarization than other quasars, reinforcing the view that they are normal quasars viewed from a more equatorial aspect. However, there is a wide distribution of polarization values, which may be due to intrinsic differences in the geometry or optical depth to scattering. No correlations are found among emission line or broad absorption line properties and continuum polarization, suggesting that these properties are regulated by internal differences unrelated to viewing angle. The continuum polarization of BAL QSO is weakly wavelength dependent after correction for emission line dilution. In most objects, the polarization rises to the blue, suggesting that dust scattering or absorption may be important.
\r\n\r\nBroad emission line photons are polarized less than the continuum; and the position angle of the electric vector is rotated with respect to the continuum. The semi-forbidden C III] emission line is polarized differently than the C IV emission line in some cases, suggesting resonance scattering in the C III] emission line region. Resonantly scattered photons from the broad absorption line region are detected at high velocities red-ward and blue-ward of the C IV line center in the spectra of some objects. These photons are negatively polarized with respect to the continuum photons, showing that the broad absorption line region and the continuum scattering region are oriented perpendicular to each other.
\r\n\r\nThe polarization increases in the BAL troughs, due mainly to partial coverage of the central source by the broad absorption line region. Partial coverage of the continuum and broad emission line clouds leads to difficulties in determining the true optical depth of the BAL outflow. The geometry of the intervening BAL clouds is skewed with respect to the continuum scattering region, which results in position angle rotations in the BAL. The variation of polarization with velocity in the BAL is consistent with a non-radial, accelerating outflow of ionized gas. Our polarimetry observations are consistent with a model which unifies BAL QSO and non-BAL QSO. The BAL wind appears to occupy a narrow range of equatorial latitudes. When we view a QSO through this outflow, we see the characteristic troughs in BAL QSO.
\r\n", "doi": "10.7907/X967-5E39", "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:3345", "collection": "thesis", "collection_id": "3345", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09052008-154229", "primary_object_url": { "basename": "Chou_d_1987.pdf", "content": "final", "filesize": 2417034, "license": "other", "mime_type": "application/pdf", "url": "/3345/1/Chou_d_1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Development and Evolution of Magnetic Fields in Active Regions on the Sun", "author": [ { "family_name": "Chou", "given_name": "Dean-Yi", "clpid": "Chou-Dean-Yi" } ], "thesis_advisor": [ { "family_name": "Zirin", "given_name": "Harold", "clpid": "Zirin-H" } ], "thesis_committee": [ { "family_name": "Zirin", "given_name": "Harold", "clpid": "Zirin-H" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "Libbrecht", "given_name": "Kenneth George", "clpid": "Libbrecht-K-G" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "The purpose of this thesis is to investigate the development and evolution of magnetic fields in new active regions on the sun. The major observations are digital magnetograms of the line-of-sight component of magnetic fields made with the high sensitivity videomagnetograph at the Big Bear Solar Observatory, and H\u03b1 filtergrams with the 1/4 \u00c5 H\u03b1 Zeiss filter.
\r\n\r\nThis thesis consists of three themes. First, the separation velocity of emerging magnetic flux is investigated. I measure the separation velocities of opposite polarities of 24 new bipoles, and compare them with the theoretical values estimated by the present theory of magnetic buoyancy. The predicted velocities are higher than those observed. Second, the cooling time scale of growing sunspots is studied. I define the cooling time scale and derive it from the measurements of intensity and magnetic field strength of sunspots. The cooling time scales of the ten growing sunspots studied range from 0.5 to 9 hr. I also estimate the cooling time scale from two models, the Inhibition Model and the Alfven Wave Model, based on linear theory. Both models give cooling times of about 0.05 hr. Third, nonadiabatic effects in convective instabilities in thin flux tubes are examined. I study the convective instabilities in thin flux tubes by including a nonadiabatic term. I find that a flux tube is convectively stable for any field strength.
", "doi": "10.7907/rkc8-g529", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:3434", "collection": "thesis", "collection_id": "3434", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09102008-091002", "primary_object_url": { "basename": "Hough_dh_1986.pdf", "content": "final", "filesize": 5668667, "license": "other", "mime_type": "application/pdf", "url": "/3434/1/Hough_dh_1986.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Parsec-Scale Structure in the Nuclei of Double-Lobed Radio Quasars", "author": [ { "family_name": "Hough", "given_name": "David Hans", "clpid": "Hough-David-Hans" } ], "thesis_advisor": [ { "family_name": "Readhead", "given_name": "Anthony C. S.", "orcid": "0000-0001-9152-961X", "clpid": "Readhead-A-C-S" } ], "thesis_committee": [ { "family_name": "Readhead", "given_name": "Anthony C. S.", "orcid": "0000-0001-9152-961X", "clpid": "Readhead-A-C-S" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Schmidt", "given_name": "Maarten", "clpid": "Schmidt-M" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "A complete sample of double-lobed quasars is defined, which is believed to be randomly oriented and which contains many objects with central components accessible to very-long-baseline interferometry (VLSI). The purpose of defining the sample in this way is to facilitate tests of physical models proposed to explain both the compact and extended structures in extragalactic radio sources. Statistical studies of the properties of these objects on the >~ kiloparsec scale are consistent with the assumption of random orientations and the simple relativistic beaming theory.
\r\n\r\nThe central components of six double-lobed quasars have been mapped at high resolution and high sensitivity with VLBI. Each object exhibits a double or extended structure on the the ~parsec scale. This structure can be interpreted as a \"core-jet,\" the same morphology found in the dominant cores of powerful flat-spectrum sources, thus indicating a relation between the two classes of compact radio source. The presumed VLBI jets are all fairly well aligned with >~kiloparsec-scale, one-sided jets. The fact that the VLBI and large-scale jets always lie on the same side of the compact core suggests the same cause for the asymmetric structure on both scales.
\r\n\r\nThe central components of 3C245 and 3C263 have been mapped at three epochs. We find superluminal expansion in 3C263 with an apparent velocity of ~1.5c, and argue that there is evidence that 3C245 will also be found to be superluminal. These results are consistent with the simple beaming theory. It is thus clear that we will be able to measure component motion in many of these objects, which will permit us to distinguish among alternative theories of parsec-scale structure and motion.
\r\n\r\nThe future study of these compact central components will benefit greatly from the increased resolution afforded by both higher frequency, ground-based VLBI and VLBI using a radio telescope in Earth orbit.
\r\n", "doi": "10.7907/8P47-SM58", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:3405", "collection": "thesis", "collection_id": "3405", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-083654", "primary_object_url": { "basename": "Filippenko_av_1984.pdf", "content": "final", "filesize": 9870292, "license": "other", "mime_type": "application/pdf", "url": "/3405/1/Filippenko_av_1984.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Physical Conditions in Low-Luminosity Active Galactic Nuclei", "author": [ { "family_name": "Filippenko", "given_name": "Alexei Vladimir", "orcid": "0000-0003-3460-0103", "clpid": "Filippenko-Alexei-Vladimir" } ], "thesis_advisor": [ { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" } ], "thesis_committee": [ { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "Oke", "given_name": "J. Beverly", "clpid": "Oke-J-B" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Mould", "given_name": "Jeremy R.", "orcid": "0000-0003-3820-1740", "clpid": "Mould-J-R" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "Caltech Distinguished Alumni Award" }, { "literal": "div_pma" } ], "abstract": "Physical conditions in the nuclei of emission-line galaxies are investigated by analyzing their continua and optical emission lines.
\r\n\r\nThe strength and shape of the nonstellar continuum is derived for nine Seyfert galaxies. As in QSOs, it is described by a power law with slope ~ -1.1, and in the most luminous objects it flattens at blue and UV wavelengths. Even at minimum brightness it has no short-wavelength cutoff near 1 \u03bcm, eliminating the possibility that the near-infrared flux is dominated by thermal emission from hot dust grains.
\r\n\r\nA detailed analysis at optical and X-ray energies demonstrates that gas in the nucleus of NGC 7213 is photoionized by nonstellar radiation, even though it also exhibits the spectral characteristics of galaxies thought to be heated by shocks. After careful removal of the strong stellar component, it is shown how these \"shock\" features are actually more consistent with photoionization. The key is a large range of densities (~ 103-107cm-3) in the narrow-line clouds, and a fairly low ionization parameter.
\r\n\r\nSimilar studies of three additional galaxies confirm these results and strengthen the hypothesis that gas in LINERs (\"low ionization nuclear emission-line regions\") is photoionized rather than shock-heated. A tight correlation is found between the width of forbidden lines and their critical density. Moreover, much of the ionizing radiation is probably produced by a hot (T ~ 104-105 K) accretion disk.
\r\n\r\nA sensitive survey indicates that ~ 30-40% of LINERS exhibit weak, broad H\u03b1 emission. The emission-line intensity ratios are consistent with photoionization by a nonstellar continuum, indicating the presence of activity similar to (but much milder than) that of QSOs in a significant fraction of all nearby galaxies.
\r\n\r\nRelative intensities of emission lines in the narrow-line X-ray galaxy NGC 7314 are typical of type 2 Seyferts, but their widths (FWHM ~ 120-150 km s-1) are remarkably small. Thus, nonstellar radiation need not be associated with rapid motions among the narrow-line clouds. The profile of the broad H\u03b1 emission suggests that gas flows ballistically away from the nucleus. Dust, which heavily reddens radiation from broad-line clouds, is probably located within or near the clouds themselves.
\r\n", "doi": "10.7907/34v9-vc35", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:3409", "collection": "thesis", "collection_id": "3409", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-093723", "primary_object_url": { "basename": "Simon_rs_1983.pdf", "content": "final", "filesize": 4341639, "license": "other", "mime_type": "application/pdf", "url": "/3409/1/Simon_rs_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Nuclear Structure of Quasars at 329 Megahertz", "author": [ { "family_name": "Simon", "given_name": "Richard Stanley", "clpid": "Simon-Richard-Stanley" } ], "thesis_advisor": [ { "family_name": "Readhead", "given_name": "Anthony C. S.", "orcid": "0000-0001-9152-961X", "clpid": "Readhead-A-C-S" } ], "thesis_committee": [ { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "Schmidt", "given_name": "Maarten", "clpid": "Schmidt-M" }, { "family_name": "Readhead", "given_name": "Anthony C. S.", "orcid": "0000-0001-9152-961X", "clpid": "Readhead-A-C-S" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "In the four chapters in this thesis are presented studies of compact quasars using Very Long Baseline Interferometry at 329 MHz.
\r\n\r\nThe first chapter presents hybrid maps of two quasars, 3C147 and 3C286, made at 329 MHz from VLBI observations taken in 1975 with a three station interferometer. The observations presented in the first chapter were used to make the first detailed maps of compact radio structure at this frequency. Both objects consist of an unresolved core; an extended, asymmetric jet; and an even larger, completely resolved halo. For 3C147 it is possible to decompose the spectrum into individual component spectra; at 329 MHz the core of 3C147 is found to be strongly self-absorbed. For both sources the spectral index decreases monotonically from core to jet to halo.
\r\n\r\nThe second chapter presents further observations of quasars at 329 MHz. These observations were taken with a seven-station interferometer and were used to produce high dynamic range maps of the quasars 3C48, 3C147, 3C309.1, 3C380, and 3C454.3. These maps, made with the most extensive low-frequency VLBI observations to date, are the first reliable, high dynamic range maps at this frequency, and reveal extremely complex source structure in four of these sources. All five of the objects are seen to have asymmetric structure that can be interpreted in the \"core-jet\" picture of compact extragalactic radio sources. The jets observed in these objects are not straight, but bent; three of these quasars have bends in their structure greater than 90\u00b0 on scales of 1 - 10 kpc.
\r\n\r\nChapter three deals with the analysis of the two maps of 3C147 presented in chapters 1 and 2. Comparison of those maps reveals that the core of 3C147 is a low-frequency variable radio source which has brightened by a factor of two in six years. In combination with X-ray observations this is used to demonstrate that bulk relativistic motion is taking place within the core and leads to the prediction that 3C147 is a member of the class of \"superluminal\" radio sources. It is also found that the inclination to the line of sight of the underlying bulk relativistic motion is less than 10\u00b0.
\r\n\r\nA self-consistent picture of 3C147 as a low-frequency variable is thus developed which is consistent with the available observations, yet does not require an extreme value of the total energy: the total energy of the core of 3C147 is found to be ~1054 ergs. Together with NRAO 140 there are now two extragalactic low-frequency variable radio sources in which bulk relativistic motion has been demonstrated. Thus it may well be that bulk relativistic motion is responsible for the required time-scales in most, if not all, low-frequency variables.
\r\n\r\nIn chapter four, the observations presented in chapter two of 3C48, 3C147, 3C309.1, 3C380 and 3C4S4.3 are analyzed using standard synchrotron emission theory in order to discover the physical conditions occurring in these objects. For 3C48, the suggestion in chapter 2 of this source as a \"core-jet\" source is seen to be reasonable with fields energy density and pressure all decreasing with increasing distance from the supposed core. For 3C48, the suggestion in chapter 2 of this source as a \"core-jet\" source is seen to be reasonable, with fields, energy density, and pressure all decreasing with increasing distance from the supposed core. The pressure in the jet in 3C48 is extremely large, implying that the jet cannot be confined by external gas pressure, unless the surrounding medium has extreme values of the temperature and density. In the case of 3C147 (which was analyzed extensively in chapter 3), the halfwidth of the observed jet implies that collimation of the jet is occurring; the jet in 3C147 is definitely not a \"free\" jet. For 3C309.1, the 329 MHz observations give an upper limit to the turnover frequency for synchrotron self-absorption significantly lower than that available up to now; this limit, in combination with Einstein X-ray observations of 3C309.1, implies that bulk relativistic motion is occurring within the core of 3C309.1. Thus, the core of 3C309.1 may be very similar to the core of 3C147, and is a candidate for being both a superluminal source and a low-frequency variable. For 3C380 and 3C454.3, the limited spectral information available allows broad limits to be put on their properties.
\r\n", "doi": "10.7907/zyfw-8c64", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:3392", "collection": "thesis", "collection_id": "3392", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09082008-142312", "primary_object_url": { "basename": "Pier_jr_1983.pdf", "content": "final", "filesize": 3780820, "license": "other", "mime_type": "application/pdf", "url": "/3392/1/Pier_jr_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "A Study of A- and B-Type Stars in the Southern Galactic Halo", "author": [ { "family_name": "Pier", "given_name": "Jeffrey Ross", "clpid": "Pier-Jeffrey-Ross" } ], "thesis_advisor": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" } ], "thesis_committee": [ { "family_name": "Greenstein", "given_name": "Jesse L.", "clpid": "Greenstein-J-L" }, { "family_name": "Mould", "given_name": "Jeremy R.", "clpid": "Mould-J-R" }, { "family_name": "Preston", "given_name": "George W.", "clpid": "Preston-G-W" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "A sample of over 200 stars of spectral types A and B has been selected for study. Drawn from the Preston and Shectman objective-prism survey of the southern galactic halo, the stars comprise a sample of halo objects selected without kinematic bias. Photoelectric UBV photometry has been obtained and the sample stars have apparent V magnitudes mostly in the range 13.5 \u2264 V \u2264 15.5. The (U-B)--(B-V) two-color diagram shows that the halo AB stars have colors similar to those of globular cluster blue horizontal-branch (BHB) stars.
\r\n\r\nReticon spectroscopy of the sample confirms the BHB status of the large majority of the sample. Interesting non-BHB stars found include a few high luminosity A stars, several stars of low metallicity and apparently normal main-sequence gravities which may be field Population II blue stragglers, and ten metallic-line stars. A few normal A stars have been found as far as 2 to 3 kpc from the plane, but none beyond that distance. It is suggested that the metal-rich early-type population found by other authors belongs to a population of old disk stars with a scale height of over 1 kpc.
\r\n\r\nInterstellar Ca II K lines are found in many of the high-velocity stars. The interstellar components arise from low-velocity material associated with the disk.
\r\n\r\nThe solar motion of the halo AB stars is -236 \u00b1 39 km s-1 and the velocity ellipsoid is elongated towards the galactic center throughout the halo. By adding a list of halo objects drawn from other sources and solving for the solar motion a lower limit of -208 \u00b1 20 km s-1 is set for the circular velocity at the solar radius. The solar motion solution is found to be metallicity-dependent. Anisotropy in the velocity ellipsoid is strongly indicated for the combined halo objects. The presence of this global anisotropy removes one of the arguments favoring a flattened halo. Since the gravitational potential of the disk increases the z component of velocity it is seen that at very early times in the history of the Galaxy the velocities were highly anisotropic (predominantly radial).
\r\n", "doi": "10.7907/s939-dc28", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:3389", "collection": "thesis", "collection_id": "3389", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09082008-130459", "type": "thesis", "title": "Visible and Infrared Studies of Cataclysmic Variable Stars", "author": [ { "family_name": "Berriman", "given_name": "Graham Bruce", "orcid": "0000-0001-8388-534X", "clpid": "Berriman-Graham-Bruce" } ], "thesis_advisor": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" } ], "thesis_committee": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Oke", "given_name": "J. Beverly", "clpid": "Oke-J-B" }, { "family_name": "Persson", "given_name": "Eric", "orcid": "0000-0003-0554-7083", "clpid": "Persson-Eric" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "The purpose of this Thesis is to investigate the infrared properties of Cataclysmic Variable Stars, in particular, to develop the techniques needed to study the contributions to the infrared light of the red dwarf and the accretion disc around its white dwarf companion. A particular requirement of these techniques is that they do not rely on a model of the poorly understood discs. They can be applied not only to Cataclysmic Variable Stars, but also to other interacting systems containing a red star, such as symbiotic stars.
\r\n\r\nAnalysis of the visible to infrared colours of fourteen largely uneclipsing systems, based on flux ratio diagrams, shows that the red dwarfs and the opaque gas in the disc supply most of the infrared light, but the contributions of each vary widely from system to system, with more light coming from the red dwarfs in the longer period systems than in the shorter period ones. For nearly all the systems studied, upper limits can be found to the fluxes of the red dwarfs that are approximately independent of spectral type and of the conditions in the accretion discs.
\r\n\r\nIn highly inclined systems, measurements of the amplitudes of the tidally induced ellipsoidal variations of the red dwarfs provide a more precise measure of the proportion of light coming from the red dwarf. A technique to simulate the light curves of tidally distorted red dwarfs successfully accounts for the infrared light curves of U Geminorum, a system in which the red dwarf supplies nearly all the infrared light.
\r\n\r\nCompleting the Thesis is a visible and infrared study of the eclipsing dwarf nova OY Carina in quiescence. This system has been studied because in the visible, the red dwarf is seen to eclipse the white dwarf. Analysis of these eclipses, based on the assumption that the red dwarf fills its Roche Lobe, allows the determination of several fundamental properties of the system: the inclination of the system is 73.5\u00b0 to 81\u00b0, the mass of the white dwarf lies in the broad range 0.4-1.4 M\u2299 and the red dwarf lies either on or slightly below the Main Sequence mass radius relation. The principal source of uncertainty in the analysis is that the semi-amplitude of the radial velocity variations of the white dwarf is poorly known. The infrared light curves show an eclipse of the disc and, half a cycle later, a secondary minimum produced by the ellipsoidal variations of the red dwarf and its eclipse by the disc. The depth of this minimum and the colours of the system imply that the red dwarf supplies approximately one-half of the uneclipsed light of the system and that it eclipses more than three-fifths of the light of the disc. The latter result requires that the K magnitude of the red dwarf lies in the range 14.2 to 14.7. The distance to the system, as deduced from these limits and an estimate of the surface brightness of the red dwarf lies in the range 100 to 300pc. The infrared light of the disc comes largely from optically thin emission; the opaque gas occupying most of the disc does not supply much of infrared light because the disc is atypically small and more highly inclined compared with other systems.
", "doi": "10.7907/psse-c523", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:3331", "collection": "thesis", "collection_id": "3331", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09042008-141513", "primary_object_url": { "basename": "Cimerman_m_1980.pdf", "content": "final", "filesize": 2558298, "license": "other", "mime_type": "application/pdf", "url": "/3331/1/Cimerman_m_1980.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "A Study of Hydroxyl Masers in the Circumstellar Envelopes of Long Period Variable Stars", "author": [ { "family_name": "Cimerman", "given_name": "Menachem", "clpid": "Cimerman-Menachem" } ], "thesis_advisor": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "Wannier", "given_name": "Peter G.", "clpid": "Wannier-P-G" } ], "thesis_committee": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Wannier", "given_name": "Peter G.", "clpid": "Wannier-P-G" }, { "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": "The 18 cm wavelength maser radiation from long period variable (LPV) stars is emitted by hydroxyl (OH) molecules in the expanding circumstellar envelopes. The four possible transitions within the ground state of the OH molecule are divided into two groups: mainlines at 1665 and 1667 MHz and satellite lines at 1612 and 1720 MHz. Three of these lines are observed in maser radiation from LPV stars: the 1612 MHz line and the mainlines. The observed properties of the 1612 MHz radiation are easier to interpret than those of the mainlines due to the quantum mechanical symmetries of the OH molecule. This investigation tackles the problem of the OH mainline masers, first by radio observations of two LPV sources with unique OH properties, and then by a theoretical analysis.\r\n\r\nThe U Ori OH masers were monitored following the drastic events in these masers in early 1974. The events consisted of the sudden appearance of strong 1612 MHz radiation, coincident with the disappearance of the 1667 MHz radiation. They are interpreted in light of the monitored evolution of the 1612 MHz radiation, the decline in its output level, and the subsequent re-emergence of a 1667 MHz line. The conclusion is that the events are the outcome of a short-lived disturbance in the stellar photosphere, most likely a shock-wave, which affected the maser through radiative coupling between the photosphere and the OH molecules.\r\n\r\nObservations of the OH maser in W Hya are presented, which suggest an explanation of their unique polarization characteristics. The maser lines may be formed at a distance of ~ 10[superscript 14] cm from the stellar surface in the presence of a magnetic field of ~ 9 milligauss. This magnetic field is coupled to the ionized component of the outflowing circumstellar envelope. In the W Hya case the magnetic field is evident in the strong polarization, Zeeman pattern and differential magnetorotation. However, it may exist unnoticed in other OH sources, and contribute to the pumping mechanism.\r\n\r\nThe pumping of OH masers in late-type-variables by direct stellar radiation of 2.8\u03bc is studied. Two pumping schemes are suggested based on line coincidences between OH V=0-1 transitions and strong H[subscript 2]0 \u03c5[subscript 3] transitions. The water molecules perturb the stellar radiation by absorption, and thus cool the coinciding OH transition. It is demonstrated that this cooling is capable of producing strong OH masers in the circumstellar envelopes of late-type-variables. This model can account for the existence of mainline (\u0394F=0) OH masers, which is hard to explain otherwise.", "doi": "10.7907/zsta-x423", "publication_date": "1980", "thesis_type": "phd", "thesis_year": "1980" }, { "id": "thesis:3231", "collection": "thesis", "collection_id": "3231", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08262008-113619", "type": "thesis", "title": "The Structure of Hydroxyl Masers and Circumstellar Envelopes of Long Period Variable Stars", "author": [ { "family_name": "Reid", "given_name": "Mark Jonathan", "orcid": "0000-0001-7223-754X", "clpid": "Reid-Mark-Jonathan" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" }, { "family_name": "Preston", "given_name": "George W.", "clpid": "Preston-G-W" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Long period variable stars with envelopes of circumstellar dust and gas often exhibit strong hydroxyl (OH) maser emission. This emission is characterized by two emission line complexes typically separated by 20 km/s. While the OH maser spectra suggest well defined dynamical properties of the circumstellar material, the crucial observations required to determine these properties have been lacking. This thesis is primarily concerned with determining the radial velocity of the central star and the spatial distribution of the maser emission in the circumstellar material.
\r\n\r\nThe radial velocity of the central star can be determined by a statistical analysis of spectral line velocities in an ensemble of stars. Such an analysis is presented in Chapter I for optical emission and absorption lines and for radio OH maser emission lines. The results indicate that, contrary to currently accepted theories, the optical absorption line velocities and the high velocity OH emission line velocities are red-shifted with respect to the stellar radial velocity. This argues against models of the OH emission which involve shock fronts or emission from the limb of a spherically expanding circumstellar shell.
\r\n\r\nThe spatial distribution of the maser emission can be determined from radio interferometric observations. Spectral-line very long baseline (VLB) interferometric observations of the OH maser emission in long period variable stars such as IRC+F10011, U Ori and R Aql are presented in Chapter II. The primary result of these observations is that the apparent sizes of the OH maser components in long period variable stars are greater than or about 5 x 1015 cm. These large apparent sizes argue strongly against either gravitational collapse or rotation as the dominant dynamical process in the circumstellar envelope. Analysis of data obtained on IRC+10011 and VY CMa (discussed in Chapter III) indicate that the two emission complexes probably are separated by distances less than, or comparable to, the extent of the emission in either complex. These and other findings suggest that OH emission from long period variable stars comes from a series of concentric, inhomogeneous, circumstellar shells expanding from the central star. The origin of these shells is probably a result of condensation of dust followed by radiative acceleration away from the star during the stellar light cycle.
\r\n\r\nA direct Fourier inversion of VLB data is presented in Chapter III for the 1612 MHz OH emission of VY CMa. This is the first attempt at such an analysis procedure for any VLB observations. This work demonstrates that Fourier inversion of spectral-line VLB data, even with very limited u-v coverage, is more efficient and less biased than direct model fitting for the resolution of complex source structures.
\r\n", "doi": "10.7907/4EGT-TW53", "publication_date": "1976", "thesis_type": "phd", "thesis_year": "1976" } ]