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:3770", "collection": "thesis", "collection_id": "3770", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09252008-135215", "primary_object_url": { "basename": "Putney_a_1996.pdf", "content": "final", "filesize": 29149505, "license": "other", "mime_type": "application/pdf", "url": "/3770/1/Putney_a_1996.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Magnetic white dwarf stars", "author": [ { "family_name": "Putney", "given_name": "Angela", "clpid": "Putney-A" } ], "thesis_advisor": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "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.\r\n\r\n\r\nThree aspects of magnetic white dwarf stars are studied to aid in the understanding of stellar evolution.\r\n\r\nA survey of ~ 50 DC white dwarf stars was conducted in circular spectropolarimetry to search for magnetic fields [...] 30 kG. Four DC stars were discovered with magnetic fields above 30 kG: G 111-49 with B[subscript e] ~ \u2014220 MG, G 183-35 with B[subscript e] = +6.8 \u00b1 0.5 MG, G 256-7 with B[subscript e] = +4.9 \u00b1 0.5 MG, and G 234-4 with B[subscript e] = +39.6 \u00b1 11.6 kG. A new magnetic DB white dwarf was also discovered, LB 8827 with B[subscript e] = 1.0 \u00b1 0.5 MG. A total of 15% of the white dwarfs in the survey have a magnetic field > 30 kG. This value is far larger than the 2% of DA stars, but more than half of the DC stars were originally misclassified. Only 5% of the re-classified DC stars have magnetic fields above 30 kG.\r\n\r\nThree magnetic stars from the DC white dwarf survey were re-observed to investigate the possibility of rotation. Two are definitely rotating: LHS 1734 with 16 min [...] P < 1 yr and G 158-45 (=LHS 1044) with a probable period P ~ 11 hr but a definite period P [...] 1 d or P ~ a few days. G 183-35 might be rotating with 50 min [...] P < a few yr. From all the white dwarf rotations known, it is clear that angular momentum is lost before a star becomes a white dwarf, but not clear that the loss is greatly enhanced by magnetic fields.\r\n\r\nThe isolated magnetic white dwarfs G 99-47, KUV 813-14 (KUV 23162-1220), and G 227-35 were observed in linear and circular spectropolarimetry and then compared to calculated theoretical spectra to find a model for the magnetic field strength and structure. The comparisons were to Stokes' V/I (circular polarization) spectra in addition to total flux F[...], and these add many constraints to the possible solutions. An off-centered dipole or a dipole+quadrupole configuration best fits the observations.\r\n\r\nThe results of the survey and the modeling are consistent with the theory that the magnetic Ap stars are the predecessors of magnetic white dwarfs.\r\n", "doi": "10.7907/mq60-yx71", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:3406", "collection": "thesis", "collection_id": "3406", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-084712", "primary_object_url": { "basename": "Biretta_ja_1986.pdf", "content": "final", "filesize": 5046156, "license": "other", "mime_type": "application/pdf", "url": "/3406/1/Biretta_ja_1986.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Investigations of Radio Jets in M87, 3C273, and 3C345", "author": [ { "family_name": "Biretta", "given_name": "John Anthony", "clpid": "Biretta-John-Anthony" } ], "thesis_advisor": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "We present observational studies of extra-galactic radio jets in M87, 3C273, and 3C345.
\r\n\r\nObservations of the M87 jet were made at 15 GHz with 0.12\" resolution. All of the knots are clearly resolved both along and across the jet. Most of the knots are found to be smooth in appearance with no evidence of shocklike discontinuities. The brightest knot and the innermost knot are exceptions to this. The brightest knot (knot A) seems consistent with a shock caused by unsteady flow in the jet. Models for this feature are discussed. Combining our data with X-ray data suggests that the jet is neither freely expanding, thermally confined, nor ram pressure confined. The jet may, however, be magnetically confined.
\r\n\r\nWe present 10.7 GHz VLBI observations of 3C273 with high north-south resolution. A strong, non-monotonic curvature is found in the jet at projected radii \u2264 5 pc. It is unlikely that this curvature can be caused by precession. Measurements of the core size show that bulk relativistic motion in the core is not required for consistency with the observed x-ray flux.
\r\n\r\nFor 3C345 we present a systematic analysis of VLBI observations at 2.3, 5.0, 10.7, 22.2, and 89 GHz. Epochs are from 1979.25 through 1984.11. A newly ejected superluminal component (C4) is observed to accelerate, change position angle, undergo a large flux outburst, and have a flat spectrum. Older components C2 and C3 have different speeds, different position angles, and show little or no acceleration. The spectrum of C3 steepens as its flux decays. There are spectral index gradients such that both C4 and C3 are farther from the \"core\" at higher frequencies. The moving components define an opening angle of ~27\u00b0 and also show direct evidence for expansion. The counter-jet to jet flux ratio is extremely small, -0.007\u00b10.007.
\r\n\r\nThese data for 3C345 are interpreted in terms of simple models involving spherical components or shocks in a relativistic jet. All of the emission regions show evidence for bulk relativistic motion with \u03b4 > 3. The particle energies and pressures dominate those of the magnetic fields, unless \u03b4 \u2265 20. If the emission regions consist of an electron-proton plasma, then the density of thermal electrons is much less than the density of relativistic electrons. The fluxes decay with time much more rapidly than the synchrotron half-life, but much more slowly than predicted by adiabatic expansion. An attractive model for the observed kinematics identifies the emitting regions as shocks in an apparently broad and curved jet; a curvature of \u2265 3\u00b0 and \u03b3 \u2265 10 is required.
\r\n", "doi": "10.7907/dsst-qp22", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "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:3342", "collection": "thesis", "collection_id": "3342", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09052008-131956", "primary_object_url": { "basename": "Romney_jdm_1979.pdf", "content": "final", "filesize": 3258298, "license": "other", "mime_type": "application/pdf", "url": "/3342/1/Romney_jdm_1979.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Fine-Scale Structure of the Neutral Hydrogen Absorption in NGC1275", "author": [ { "family_name": "Romney", "given_name": "Jonathan Daniel MacLeish", "clpid": "Romney-Jonathan-Daniel-MacLeish" } ], "thesis_advisor": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "The high-velocity 21-cm absorption feature in NGC1275 (=3C84) has been mapped at an angular resolution of a few milliarcseconds with an intercontinental very-long-baseline interferometer. The method of analysis makes use of both the absolute amplitude of the visibility function in the continuum, and the relative amplitude and phase between the line and continuum.\r\n\r\nFine-scale structure in the continuum is determined from the observations, and the 21-cm structure of 3C84 on angular scales covering almost six orders of magnitude is reviewed.\r\n\r\nThe HI absorption is found to arise in a cloud covering part of the intense, compact continuum nucleus. Although absorption is seen against the brightest part of the continuum structure, the cloud is displaced to the northeast from the nucleus, reaching optical depths of at least 0.83. The cloud is at least 5.6 pc in diameter, with a deduced volume density between 12 and 120 cm[superscript -3].\r\n\r\nTwo basic hypotheses which have been advanced to elucidate the 21-cm absorption and other high-velocity features in NGC1275 are discussed. The results of the present investigation strongly support the interpretation that all the high-velocity features arise in a superposed galaxy in the Perseus Cluster. The alternative model, in which the high-velocity gas is ejected from the active nucleus, is inconsistent with the structure observed in the HI absorption.\r\n", "doi": "10.7907/ytaj-x179", "publication_date": "1979", "thesis_type": "phd", "thesis_year": "1979" }, { "id": "thesis:2555", "collection": "thesis", "collection_id": "2555", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06112008-140732", "primary_object_url": { "basename": "Shaffer_db_1974.pdf", "content": "final", "filesize": 3355470, "license": "other", "mime_type": "application/pdf", "url": "/2555/1/Shaffer_db_1974.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Structure of Compact Radio Sources at 10.7 GHz", "author": [ { "family_name": "Shaffer", "given_name": "David Bruce", "clpid": "Shaffer-David-Bruce" } ], "thesis_advisor": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "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.\r\n\r\nVery long baseline interferometry has been used to study the compact structure of seven radio sources at 10709 MHz ([...] = 2.8 cm). The observations, the first of a series, were made on April 28 - May 1, 1972, using the NRAO Mark II recording system. Antennas of the Owens Valley Radio Observatory (California), the Harvard Radio Astronomy Station (Texas), and the National Radio Astronomy Observatory (West Virginia) were used to give three baselines that greatly improved the (u,v)-plane coverage compared to the coverage of previously used single baselines. The three baselines had lengths of 119, 84, and 54x10[...] [...].\r\n\r\nThe observed sources were 3C 84, NRAO 150, OJ 287, 4C 39.25, 3C 273, PKS 2134+004, and VRO 42.22.01 (BL Lac). They were tracked by all three antennas during the time of mutual visibility, giving 8 to 11.5 hours of continuous coverage. With the maximum baseline of 119x10[...] [...] and a u-v cell size of ~40x10[...] [...], it is unlikely that we have missed any important structure information in the range 0[...]0005 to 0[...]005.\r\n\r\nFourier inversion of the observations was impossible because there was no phase calibration, and model fitting procedures were used to interpret the data. For five of the sources (NRAO 150, OJ 287, 4C 39.25, 3C 273, and VRO 42.22.01) models were found that fit the observations quite well. For 3C 84 and PKS 2134+004 no simple model could be found, but a rough idea of the source structure was still possible. For most of the sources, interferometric results at other frequencies and resolutions are consistent with the present findings, and a joint interpretation is given.\r\n\r\nFor all the sources except OJ 287 (which looks like a point source at our resolution and was used to calibrate the correlated flux density scale) and possibly NRAO 150, two or more separate components are required to match the observations. Component separations range from 0[...]0006 to 0[...]005 and their sizes from [...]0[...]0003 to ~0[...]002. Components less than ~0[...]002 contribute 0.85 or more of the total 10.7 GHz flux density for all the sources. Assuming synchrotron self-absorbed components, the magnetic fields in the compact sources are %10-3\u00b11 gauss. This value is less than the equi-partition field, and the individual components are expected to expand from particle pressure.\r\n\r\nSuggestions are given for additional observations to improve our knowledge of the structure and nature of compact sources.", "doi": "10.7907/FER5-8H88", "publication_date": "1974", "thesis_type": "phd", "thesis_year": "1974" }, { "id": "thesis:3183", "collection": "thesis", "collection_id": "3183", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08212008-100027", "primary_object_url": { "basename": "Purcell_gh_1973.pdf", "content": "final", "filesize": 5775652, "license": "other", "mime_type": "application/pdf", "url": "/3183/1/Purcell_gh_1973.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Structure of Compact Radio Sources at 606 MHz", "author": [ { "family_name": "Purcell", "given_name": "George Harber", "clpid": "Purcell-George-Harber" } ], "thesis_advisor": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Long-baseline interferometry has been used to study the structure of thirteen compact radio sources at 606 MHz. The baseline was 3324 kilometers long and nearly east-west in orientation, so that the maximum angular resolution was about a hundredth of a second of arc for each source.\r\n\r\nThere were two series of observations, made on June 29 to July 1, 1971, and February 3 to 6, 1972. For most of the sources observed in each session, the correlated flux was measured from ten to forty times over a wide range of hour angle, with a standard error for each measurement of about 0.12 flux unit. A few sources were observed less often. Simple source models were then fitted to the data and compared to the models proposed by other observers.\r\n\r\nThe data for most of the sources were found to be consistent with models containing an elliptical halo concentric with an unresolved core. 3C 147, 3C 273, and 3C 279 appear to be more complicated, however. The observations of 3C 84, 3C 279, and 3C 345 also show evidence of weak structure at relatively large distances from the strong central components.\r\n\r\nP1345+12 and CTD 93 were observed only in the first session, and 3C 120 and 3C 286 only in the second session. CTA 21, 3C 84, 3C 147, 3C 273, 3C 279, 3C 345, 3C 380, CTA 102, and 3C 454.3 were observed in both sessions, and all but CTA 21 and 3C 380 gave strong evidence of changes in flux or structure during the interim. These changes appear to be intrinsic to the sources, and not the result of instrumental effects or scintillation phenomena.\r\n", "doi": "10.7907/8jjw-z848", "publication_date": "1973", "thesis_type": "phd", "thesis_year": "1973" }, { "id": "thesis:3224", "collection": "thesis", "collection_id": "3224", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08252008-150426", "primary_object_url": { "basename": "Greisen_ew_1973.pdf", "content": "final", "filesize": 9388474, "license": "other", "mime_type": "application/pdf", "url": "/3224/1/Greisen_ew_1973.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Aperture Synthesis of Interstellar Neutral Hydrogen in Absorption", "author": [ { "family_name": "Greisen", "given_name": "Eric Winslow", "clpid": "Greisen-Eric-Winslow" } ], "thesis_advisor": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "Stanley", "given_name": "Gordon J.", "clpid": "Stanley-G-J" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "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.\r\n\r\nThe Owens Valley Radio Observatory interferometer has been used to carry out a program of aperture synthesis in the interstellar neutral hydrogen line. Maps having resolutions of 1 KHz and about 1.3 arc minutes have been produced using a novel Fourier inversion procedure which is discussed in some detail. The equipment, observing procedure, noise, and gaussian analysis of spectra are also treated.\r\n\r\nThe Perseus arm feature in the spectrum of Cygnus A is of low optical depth but reveals considerable spatial structure. The data suggest that the hydrogen is located in a thin shell expanding at 2 km/sec, with a radius around 9.7 parsecs and a total mass of 175 solar masses. The Perseus arm feature in the spectrum of Cassiopeia A contains very large amounts of hydrogen with extremely complicated spatial structure. The results may be explained qualitatively by the two-arm spiral shock model of the Galaxy. The principal component in the spectrum of the Crab Nebula is found to show a considerable velocity gradient across the source and appears to contain several condensations within a large, less dense cloud. The absorption feature in the spectrum of 3C353 appears to have a gradient in the dispersion of one component. If real, this result suggests scale lengths in the interstellar hydrogen as small as 0.14 parsecs. The absorption spectra of W12, 3C147, Cygnus A (local arm), and 3C123 are also discussed briefly.\r\n\r\nUpper limits to the temperature as low as 50\u00b0K are found for some of the spectral components although upper limits between 80 and 160\u00b0K are more common. Hydrogen clouds with diameters about 1 parsec and densities on the order of 100 cm[\u2026] are shown to be common. The implications of these results for the two-phase model of the interstellar medium are discussed.\r\n", "doi": "10.7907/3A2K-C664", "publication_date": "1973", "thesis_type": "phd", "thesis_year": "1973" } ]