MS, University of Cincinnati, 2001, Arts and Sciences : Physics

Radio astronomy is the science of collecting extra-terrestrial radiation in the range of 15 MHz to 600 GHz to gain understanding of celestial objects. In this thesis I discuss both the single parabolic reflector radio telescope and the two-telescope radio interferometer used in radio astronomy. The total power received by a parabolic reflector is dependent on the size of the antenna, the efficiency of the reflector, the wavelength of light under observation, and the angular response of the antenna, called the "normalized power pattern". Diffraction effects limit the resolution of the single parabolic reflector. The two-telescope interferometer has increased resolution because the main beam that would be created by a single antenna is split into multiple beams through interference, with the width of one beam corresponding to the angular resolution of the interferometer. A commonly used typed of interferometer is the correlating interferometer that integrates the product of the voltages received at each telescope. The correlating interferometer does not measure the received power directly, but rather the Fourier transform of it called the visibility function. By taking many measurements with different baselines, the visibility function can be sampled over the Fourier transform (or u-v plane) space. The visibility function can then be inverted to create a radio map of the brightness distribution of the source.

Committee: Randy Johnson (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, University of Toledo, 2006, Physics

The Mars Global Surveyor Mars Orbiter Camera obtained global maps of the Martian surface with equatorial resolution of 7.5 km/pixel in two wavelength ranges: blue (400-450 nm) and red (575-625 nm). The maps used were acquired between March 9, 1999 (Ls=107.7°) and May 31, 2003 (Ls=194.5°), corresponding to approximately two and a quarter Martian years. Using the global maps, cloud area was measured daily for water-ice clouds topographically corresponding to Alba Patera, Olympus, Ascraeus, Pavonis, Arsia, and Elysium Mons. Seasonal trends in cloud activity have been established for each volcano. For volcanoes other than Arsia Mons, interannual variations that could be associated with the 2001 planet-encircling dust storm are minimal. At Arsia Mons, where cloud activity was continuous in the first two years, clouds disappeared totally for ~ 85° of Ls (Ls=188°-275°) due to the dust storm. The altitudes of several of these clouds have been measured from the locations of the visual cloud tops and cloud center locations were determined. We use MOC wide-angle blue (425 nm) images supported by a 3-component (surface, cloud layer, dust layer) radiative transfer model to retrieve and map water-ice cloud properties. TES dust measurements are incorporated into the model after adjusting for wavelength and correcting for topography. Surface reflectance is inferred from MOC images of the same locations acquired during cloud free periods with minimum dust loading. We chose six aphelion-season MOC image strips, two each for Olympus, Ascraeus, and Elysium Mons, that exhibit well-defined clouds and include TES cloud opacity measurements within the MOC field of view. The resulting maps of 425 nm cloud optical depth reveal large opacity gradients at spatial scales of 10-20 km. Maximum cloud opacity lies between 0.7 and 0.8 for Elysium Mons, 0.8 and 0.9 for Ascraeus Mons, and exceeds 1.0 at Olympus Mons. The largest optical depths lie along the volcano flanks below the summit, and the sma (open full item for complete abstract)

Committee: Philip James (Advisor) Subjects: Physics, Astronomy and Astrophysics

Master of Science, University of Toledo, 2006, Physics

Deneb is the prototype type A2 supergiant. Unfortunately, the literature detailing the variability of A-tpye supergiants is sparse. We are analyzing 339 spectra in the H-alpha wavelength region obtained at Ritter Observatory taken over the five-year span from 1997 through 2001. We also obtained during the same time period, 370 Stromgren photometric measurements at the Four College Automated Photoelectric Telescope. The H-alpha profile of Deneb exhibits a characteristic P Cygni profile, consistent with mass-loss in Deneb. Dynamical spectra of the H-alpha profile were constructed to visually search for cyclic variability in the wind of the star. No clear evidence was found for this type of behavior. Time?series analysis was performed to analyze the H-alpha net equivalent widths, radial velocities, and photometry using the CLEAN algorithm.

Committee: Nancy Morrison (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, University of Toledo, 2005, Physics

While rapid rotation is likely the dominant mechanism which influences the development of classical Be circumstellar disks, recent observational and theoretical work suggest that evolutionary age and/or metallicity may also influence the onset of the Be phenomenon. We use a simple 2-color diagram photometric technique to identify the candidate Be population in 16 Large Magellanic Cloud (LMC), Small Magellanic Cloud (SMC), and Galactic clusters having a wide range of ages and metallicities. We detect an enhancement in the fractional early-type candidate Be star population relative to the fractional later-type candidate population in clusters whose early-type stars are near the end of their main sequence lifetimes, suggesting the Be phenomenon is enhanced with evolutionary age. Furthermore, in contrast to the suggestion of Fabregat & Torrejon (2000) that the Be phenomenon should begin at least 10 Myr after the zero-age-main-sequence, we detect a substantial number of candidate Be stars in clusters as young as 5 Myr. Follow-up photo-polarimetric observations of these young candidates reveal many are true classical Be stars, indicating that a significant number of zero-age-main-sequence stars must be rotating close to their critical breakup velocities. The improved statistics offered by our study also reveal clear evidence of an enhancement of the Be phenomenon in low metallicity environments. It is commonly assumed in the literature that all B-type objects detected as excess H alpha emitters via 2-color diagrams are ''Be stars''. We explore the nature of many of these candidate Be stars with additional photo-polarimetric observations, and find that ~25% of these objects exhibit properties which aren't consistent with those expected from classical Be stars. We also find that the prevalence of polarization Balmer jumps in Be stars located in low metallicity environments is lower than that typically observed for Galactic Be stars. One interpretation of this result is that (open full item for complete abstract)

Committee: Karen Bjorkman (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, University of Toledo, 2005, Physics

In this dissertation, we report on our study of interstellar dust through the process of photoluminescence (PL). We present the discovery of a new band of dust PL, blue luminescence (BL) with λpeak ~ 370 nm in the proto-planetary nebula known as the Red Rectangle (RR). We attribute this to fluorescence by small, 3-4-ringed polycyclic aromatic hydrocarbon (PAH) molecules. Further analysis reveals additional independent evidence for the presence of small PAHs in this nebula. Detection of BL using long-slit spectroscopic observations in other ordinary reflection nebulae suggests that the BL carrier is an ubiquitous component of the ISM and is not restricted to the particular environment of the RR. We present the spatial distribution of the BL in these nebulae and find that the BL is spatially correlated with IR emission structures attributed to aromatic emission features (AEFs), attributed to PAHs. The carrier of the dust-associated photoluminescence process causing the extended red emission (ERE), known now for over twenty five years, remains unidentified. We constrain the character of the ERE carrier by determining the wavelengths of the radiation that initiates the ERE – λ < 118 nm. We note that under interstellar conditions most PAH molecules are ionized to the di-cation stage by photons with E > 10.5 eV and that the electronic energy level structure of PAH di-cations is consistent with fluorescence in the wavelength band of the ERE. In the last few chapters of the dissertation we present first results from ongoing work: i) Using narrow-band imaging, we present the optical detection of the circumbinary disk of the RR in the light of the BL, and show that the morphology of the BL and ERE emissions in the RR nebula are almost mutually exclusive. It is very suggestive to attribute them to different ionization stages of the same family of carriers such as PAH molecules. ii) We also present a pure spectrum of the BL free of scattered light, resolved into seven molecular (open full item for complete abstract)

Committee: Adolf Witt (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2007, Astronomy

Color-magnitude diagrams of resolved stellar populations, especially when combined with metal abundance patterns from spectroscopy, are our principal means of determining the evolutionary history of the Galaxy, its stellar clusters, and dwarf satellites. In turn, they also guide our ideas about stellar structure and evolution. Improvements in the capability of evolutionary models allow better interpretations of the data, and better data lead to improvements in the theory. In this dissertation, I concentrate upon the horizontal branch (HB) of composite stellar populations as an aid to understanding the ages, helium content, and mass loss history of stellar systems. Hitherto, the HB has been studied primarily in single stellar populations, such as globular clusters, by comparing observations to theoretical stellar evolutionary models. The characterization of the HB has enabled constraints to be placed upon the ages, helium content, and red giant mass loss of the globular cluster populations. There is no reason in principle why such methods cannot be applied to composite population stellar systems to disentangle their complex history. In this dissertation, I utilize stellar evolutionary modeling and specifically the morphology of the HB to investigate the hypothesized helium-rich stars in the globular cluster Omega Centauri, and similar methodology to constrain the history of the metal-poor part of the stellar population in the Galactic bulge using the metallicity distribution of RR Lyrae variables.

Committee: Donald Terndrup (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2007, Astronomy

Galaxy clustering measurement has been one of the leading tools in cosmology for estimating a more fundamental quantity, the clustering of the underlying dark matter distribution. With the recent advances in galaxy redshift surveys, and hence dramatic improvement in observational data, the main obstacle to achieving this goal has become the theoretical uncertainty of galaxy bias, the difference between the galaxy and the matter distributions. The halo occupation distribution (HOD) program has emerged as a powerful tool to overcome the difficulty in inferring dark matter clustering by providing a theoretical framework that describes statistical properties of galaxy populations in individual dark matter halos. Moreover, gravitational lensing depends only on gravity, regardless of whether it is produced by dark or luminous matter, thus providing an observational method to break the degeneracy between the galaxy bias and underlying cosmology. In particular, weak gravitational lensing uses the subtle distortion of background galaxy shapes to measure how foreground lensing matter is statistically distributed, making its method well suited to the HOD description. In this thesis, I describe three methods to quantify dark matter clustering based on the HOD framework, making full use of precision measurements of galaxy clustering and weak lensing from recent galaxy redshift surveys. First, using galaxy clustering measurements on small scales, I~infer the scale-dependent bias function, which makes it possible to extend the recovery of the primordial matter power spectrum over a large dynamic range, and thereby tighten constraints on cosmological parameters obtainable from the galaxy samples of the Sloan Digital Sky Survey. Second, I~develop an analytic model for combining galaxy-galaxy lensing and galaxy clustering to constrain the matter density parameter and the matter fluctuation amplitude. Finally, I~present a novel method to constrain dark energy models using cluster-gala (open full item for complete abstract)

Committee: David Weinberg (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2007, Astronomy

We investigate the results of reverberation-mapping mass measurements and two-dimensional (2-D) decompositions of high-resolution host galaxy images in the context of black hole scaling relationships. We present new monitoring data leading to an improved black hole mass measurements for the nearby Seyfert galaxy NGC 4151. We also present new monitoring data for the well-studied NGC 5548, which show the active galactic nucleus (AGN) in the lowest luminosity state during a monitoring campaign. We show that the mass derived from this low state is consistent with previous mass measurements, and that the virial relationship previously discovered between the width of the broad lines and their time lags relative to the continuum flux still holds. We also present complete, 2-D galaxy decompositions for 29 of the 36 objects in the reverberation-mapped sample. We create PSF-subtracted images of the host galaxies and measure the starlight contribution to the luminosity measurements from the original monitoring programs. Accounting for this contribution, we revisit the radius – luminosity relationship for AGNs and find a reduced scatter and a slope of approximately 0.5 that holds over 5 decades in luminosity. This slope is consistent with the naive expectation that all AGNs are simply scaled models of each other. Finally, we use the galaxy model parameters to investigate several black hole mass scaling relationships with host galaxy properties, namely the black hole mass – bulge luminosity relationship, the black hole mass – bulge mass relationship, and the black hole mass – Sersic index relationship. We find tight correlations for the black hole mass – bulge luminosity and black hole mass – bulge mass relationships, but these results only marginally agree with previous studies. Rather, they point to an increased black hole mass fraction at lower bulge luminosities and masses than was previously seen. Additionally, we find no evidence for the black hole mass – Sersic index rel (open full item for complete abstract)

Committee: Bradley Peterson (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2007, Astronomy

The Kilodegree Extremely Little Telescope (KELT) project is an effort to find the best way to discover planetary transits of bright stars and to implement that method by building a telescope and discovering planets. In order to learn how to design a survey for transits of bright stars, we start by constructing a model of an all-sky survey for transits. That model points to an optimal survey configuration that uses a small-aperture, wide-field telescope to search for transits of stars in the range 8 < V < 10 magnitude. We used the parameters suggested by the model to build the KELT telescope, and we have deployed it to Winer Observatory in Arizona and begun a long-term survey for planets in a series of fields around the sky. The survey area covers about 25% of the Northern hemisphere and should allow us to detect the most scientifically valuable transiting planets. We examine the performance of the telescope with a number of metrics, and we find that it is performing at the level needed to detect the types of transits we are seeking. We have completed the analysis of the first data set from KELT - a commissioning run from early 2005 that observed the Praesepe open cluster over 74 nights. We obtained lightcurves of 69,337 stars, and detected 58 long period variables and 153 periodic variables. Sixteen of these are previously known variables, yielding 195 newly discovered variables for which we provide properties and lightcurves. We also searched for planetary-like transits, finding four transit candidates. Follow-up observations indicate that three of the candidates are astrophysical false positives, with one candidate inconclusively characterized.

Committee: Richard Pogge (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2006, Astronomy

Investigations into the elemental abundances in two nearby active galaxies, the narrow-line Seyfert 1 (NLS1) Markarian 1044 and the Seyfert 1 Markarian 279, are reported. Spectra from three space-based observatories HST, FUSE, and CHANDRA, are used to measure absorption lines in material outflowing from the nucleus. I make multi-wavelength comparisons to better convert the ionic column densities into elemental column densities which are then used to determine abundances (metallicities). NLS1 galaxies are known to have extreme values of a number of properties compared to active galactic nuclei (AGNs) as a class. In particular, emission-line studies have suggested that NLS1s are unusually metal-rich compared to broad-line AGNs of comparable luminosity. To test these suggestions I perform absorption-line studies on the NLS1 Markarian 1044. I use lines of HI, CIV, NV, and OVI to properly make the photoionization correction through the software Cloudy and determine abundances of Carbon, Nitrogen and Oxygen. I find two results. The first is that Markarian 1044 has a bulk metallicity greater than five times solar. The second is that the N/C ratio in Markarian 1044 is consistent with a solar mixture. This is in direct contradiction of extrapolations from local HII regions which state N/C should scale with bulk metallicity. This implies a different enrichment history in Markarian 1044 than in the Galactic disk. I also report discovery of three new low-redshift Ly-alpha forest lines with log N HI>12.77 in the spectrum of Markarian 1044. This number is consistent with the 2.6 expected Ly-alpha forest lines in the path length to Markarian 1044. I also investigate the CHANDRA X-ray spectrum of Markarian 279, a broad-line Seyfert 1. I use a new code, PHASE, to self-consistently model the entire absorption spectrum simultaneously. Using solely the X-ray spectrum I am able to determine the physical parameters of this absorber to a degree only slightly poorer than in the multi-wavel (open full item for complete abstract)

Committee: Smita Mathur (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2006, Astronomy

In the first part of this dissertation I describe the results of a photometric and spectroscopic survey of a sample of cool, metal-poor subdwarfs in the solar neighborhood. These metal-poor stars are of interest because, as members of the Galactic halo, they give clues about the history of the Galaxy and its formation mechanisms, and may enable us to study satellites of the Milky Way and the Galactic merger history. A sample of halo subdwarfs have been selected using a reduced proper motion (RPM) diagram. Accurate and precise photometric measurements of 635 stars selected in this manner allow better definition of the RPM diagram and determination of its usefulness as a selection method. Accurate spectrophotometry yields radial velocities of the candidates as well as metallicity and temperature estimates for 288 subdwarfs. Of special interest in this sample are the ten newly discovered extremely metal-poor stars, as well as four carbon-enhanced metal-poor stars. I use these new observations to search the local Galactic halo for structure due to merger remnants and moving groups; there is some evidence for both. I also discuss the metallicity distribution function of the sample and compare it to previous work on this subject. No astronomical observations of any sort are possible without appropriate, well-calibrated instrumentation with which to perform the measurements. In the second part of this dissertation, I describe the Image Motion Compensation System (IMCS) for the Multi-Object Double Spectrograph (MODS), an optical spectrograph for the Large Binocular Telescope. The system performs closed-loop image motion compensation, actively correcting for image motion in the spectrograph's focal plane caused by large scale structural bending due to gravity as well as other effects such as temperature fluctuation and mechanism flexure within the instrument. The system is currently installed in the MODS instrument and controls instrumental flexure to within specifications. (open full item for complete abstract)

Committee: Darren DePoy (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2006, Astronomy

We target 234 galaxies for Hα spectroscopy, selected from the Sloan Digital Sky Survey spectroscopic galaxy catalog, and successfully obtain rotation curves for 162 galaxies using the Calar Alto and MDM telescopes. No morphological cuts were applied to the sample, except an i-band isophotal axis ratio of < 0.7. We fit arc-tangent functions to the rotation curves, and evaluate the circular velocity at a radius containing 80% of the total i-band light. The g, r, i, and z-band Tully-Fisher relations are determined using a maximum likelihood fitting procedure that leaves the slope, intercept, and intrinsic scatter as free parameters. The Tully-Fisher relations have slopes between -5.4 and -7.7 ± 0.2 mag/log10(kms-1), and intercepts between -18.95 and -19.88 ± 0.04 mag at 100 kms-1, and an intrinsic scatter of 0.42 ± 0.04 mag independent of wavelength. We find correlations between TF residuals and color and half-light radius residuals in the expected sense. The data weakly follow the trend expected if the stellar mass-to-light ratio was approximated by the color. We investigate the correlations among stellar mass (M*), disk scale length (Rd), and rotation velocity at 2.2 disk scale lengths (V2.2) for a sample of 81 disk-dominated galaxies. We find a logarithmic slope of 2.60 ± 0.13 for the Li-V2.2 relation, somewhat shallower than most previous studies, with intrinsic scatter of 0.13 dex. Our direct estimates of the total-to-stellar mass ratio yield a median ratio of 2.4 to 4.4, with large scatter at a given M* and Rd. The stellar mass accounts for 65% of the rotation within 2.2Rd. The distribution of scale lengths at fixed 0M* is broad, but we find no correlation between disk size and the residual from the M*-V2.2 relation. This result implies that stellar disks do not dominate the mass within 2.2Rd and have md < 0.1. A model with a disk-to-halo mass ratio md=0.05 provides a reasonable match to the Rd-M* distr (open full item for complete abstract)

Committee: David Weinberg (Advisor); Richard Pogge (Other); Barbara Ryden (Other) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2006, Astronomy

I present an investigation into the local warm-hot gaseous environment of the Milky Way as observed through highly ionized metal absorption lines in ultraviolet and X-ray spectra. These X-ray lines (primarily OVII) had been reported at redshifts consistent with zero in previous studies of background quasars; however, it has been unclear whether this gas exists close to the Galaxy (within a few tens of kpc) or extends far out into intergalactic space, thereby comprising most of the mass in the local universe. Additionally, highly-ionized OVI high-velocity clouds (HVCs), some of which are associated with the ubiquitous extended neutral hydrogen HVCs seen around the Galaxy, had been extensively studied. However, the distance to the OVI HVCs, and their relation to the X-ray lines, remained undetermined. With three of the highest-quality Chandra grating spectra of extragalactic sources to date, a large number of z=0 absorption lines are detected; the FUSE spectra of these same objects show low- and high-velocity OVI absorption. Using advanced curve-of-growth and ionization balance analysis, limits are placed on the velocity dispersion, temperature, and density of the warm-hot gas along these lines of sight. In none of these cases can the absorption be placed conclusively at Galactic or extragalactic distances. However, in two of the three cases (Mrk 421 and Mrk 279), the observed OVI UV absorption components are found to be inconsistent with the X-ray absorber, indicating that the X-ray absorption is either extragalactic or traces a previously undiscovered Galactic component. The third sightline (PKS 2155-304) exhibits absorption with properties more similar to Mrk 421 than Mrk 279; thus, there may be more than one physical process contributing to the observed absorption along any given sightline. While the X-ray components of this research exclusively employ Chandra data, the XMM-Newton mission can in principle be used for the same purpose. XMM's effectiveness in observ (open full item for complete abstract)

Committee: Smita Mathur (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2006, Astronomy

Two fundamental predictions of modern cosmological models are that i) galaxies form from small perturbations in the cosmic density field and ii) there is a tenuous medium between the galaxies that traces the underlying dark matter distribution in a relatively simple way. This thesis concerns the structure of the intergalactic medium (IGM) and its relation to galaxies. Specifically, I analyze the nature of the IGM, observable via the Lyman-alpha transition of hydrogen, as predicted from cosmological hydrodynamic simulations of a cold dark matter + dark energy universe. I first quantify the relation between galaxies and absorption in the Lyman-alpha forest on large (~10 Megaparsec) and small (~0.5 Megaparsec) scales and show that, in the absence of feedback from the galaxies themselves, observations of this relation can serve as robust tests of the inflationary cold dark matter model. I show that the strong bias of high redshift galaxies toward high density regions imprints a clear signature on the distribution of flux in the Lyman-alpha forest, and these predictions are examined as functions of galaxy baryon mass, star formation rate, and dark matter halo mass and occupation. I then investigate the potential impact of galaxies on the IGM and find that supernova-driven winds (as predicted in cosmological simulations) can substantially impact their local surroundings, particularly via heating, but that only very powerful winds can create easily detectable “holes” in the IGM. The impact of winds on the Lyman-alpha optical depth near galaxies is less dramatic than their impact on gas temperature because winds heat only a small fraction of the gas present in the turnaround regions surrounding galaxies, all of which contribute to the Lyman-alpha forest near galaxies. Finally, I combine a Monte Carlo radiative transfer code with cosmological hydrodynamic simulations to investigate the signature of fluorescent Lyman-alpha emission from large scale structure due to impinging (open full item for complete abstract)

Committee: David Weinberg (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2006, Physics

After reviewing the pillars of the concordance cosmology, which serves as the framework of this thesis, I describe how the accretion history of the Universe is revealed by thermal X-ray emission from the stellar sytems and nuclear regions of galaxies. I then go on to discuss how my collaborators and I have used this information to trace the formation of stars and the growth of supermassive black holes over the last ~ 8 Gyrs, i.e., from z ~ 1 to the present. It is of great importance for our understanding of galaxy evolution to determine whether there is a break or a continuum in these processes from the powerful quasars and starbursts of the past, to the seemingly dormant, "normal" galaxies more typical of the present epoch. To help settle the question, we combined optical data from the NOAO Deep Wide-Field Survey (NDWFS), X-ray data from the XBootes survey, and spectral information from the AGN and Galaxy Evolution Survey (AGES) in order to simultaneously obtain deep and wide coverage of the normal galaxy population. In this manner, my collaborators and I were able to bridge the gap in normal galaxy X-ray coverage between large-area local surveys and high redshift, small volume deep fields. Our findings suggest the accretion history of the Universe plays out as a continuum, with the growth of stellar populations and supermassive black holes steadily tailing off rather than abruptly ceasing as we move toward the faint end of the luminosity function.

Committee: Terry Walker (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2005, Astronomy

An investigation into the stellar and planetary content of the open cluster NGC 1245 using BVI photometry from the MDM 1.3m and 2.4m telescopes. Based on detailed isochrone fitting, I find NGC 1245 has a slightly sub-solar metallicity, [Fe/H]=-0.05± 0.08 and an age of 1.04±0.09 Gyr. I determine an extinction of Av=0.68±0.09 and a distance modulus of (m-M)o=12.27±0.12, which corresponds to a distance of 2.8±0.2 kpc. I derive a logarithmic mass-function slope for the cluster of α=-3.12±0.27, where a Salpeter slope is α=-1.35. The mass function for the inner cluster has a very shallow slope, b=-0.56±0.28. Whereas the outer periphery of the cluster is enriched with low mass members and devoid of high mass members out to the tidal radius, rt=20 arcmin (16.5 pc). Based on the observed surface-density profile and an extrapolated mass function, I derive a total cluster mass, M=1300±170 solar mass. I undertook a 19-night photometric search for transiting extrasolar planets in the cluster. An automated transit search algorithm with quantitative selection criteria finds six transit candidates; none are bona fide planetary transits. I fully analyze this null result to derive upper limits on the fraction of cluster members with close-in Jupiter-radii, RJ, companions. I characterize the survey detection probability via Monte Carlo injection and recovery of realistic limb-darkened transits for every star in the sample. The transit survey sample contains ~740 cluster members. I calculate 95% confidence upper limits on the fraction of stars with planets by assuming the planets have an even logarithmic distribution in semimajor axis over the Hot Jupiter (HJ - 3.0(open full item for complete abstract)

Committee: Darren DePoy (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2005, Astronomy

In this thesis I explore current problems of Galactic astronomy by following two distinct but complementary approaches: the kinematic and photometric properties of local stellar populations, and the theory of stellar evolution. Under the first approach, I construct the largest available catalog of genuine wide binaries (a > 100 AU) and, using the relative positions of both components on a reduced proper-motion diagram, I cleanly classify them as belonging to either the disk or the halo of the Galaxy. These samples, drawn from the Revised New Luyten Two-Tenths catalog, are complete to separations of 500 and 900 arcsec, corresponding to about 0.1 and 1 parsec, respectively. At wide separations, both distributions are well described by power laws that have, within the uncertainties, identical exponents. The fact that these distributions have similar slopes and normalizations, despite the radically different Galactic environments to which they belong today, argues for similarity of the star-formation conditions of the two populations. The fact that the halo binaries obey a single power law out to about 1 parsec permits strong constraints on halo dark-matter candidates. Using Monte Carlo simulations, we exclude a halo fully composed of MAssive Compact Halo Objects (MACHOs) more massive than 43 solar masses at 95 percent confidence. I outline the prospects for using the Sloan Digital Sky Survey in the assembly of a catalog of halo wide binaries which, by improving the statistics at large separations, will enable exploration of MACHO masses in the astrophysically important regime of heavy stellar remnants. Finally, taking advantage of the identification of faint companions of Hipparcos stars, I construct a catalog of 424 intrinsically dim (i.e., low-mass) field stars with accurate (better than 3-sigma) parallaxes. Under the approach of stellar evolution, I study the long-standing problem of abundance anomalies in red giants, concentrating in non-standard mixing processes i (open full item for complete abstract)

Committee: Andrew Gould (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2005, Astronomy

This work is dedicated to the study of the evolution of CVs and mergers of close binaries. In contrast to previous studies, this work uses modern empirical formulae for angular momentum loss by magnetized stellar winds. Two important differences with previous prescriptions include the saturation of angular momentum loss rate for fast rotators, and the existence of angular momentum loss in low mass, fully convective stars. Changes in the treatment of angular momentum loss rate have a dramatic effect on the understanding of the evolution of CVs. The timescale for angular momentum loss (J) above the fully convective boundary is ∼2 orders of magnitude longer than inferred from the older model, and the observed angular momentum loss properties show no evidence for a change in a behavior at the fully convective boundary. This provides evidence against the hypothesis that the period gap is caused by an abrupt change in the angular momentum loss law when secondary becomes fully convective and implies that the timescale for CV evolution is much longer than was thought, comparable to a Hubble time. It is demonstrated that when evolved secondaries are included, a spread in the secondary mass-orbital period plane comparable to that seen in the data is produced for either the saturated prescription for magnetic braking or the unsaturated model commonly used for CVs. It is argued that in order to explain this spread a considerable fraction of all CVs should have evolved stars as the secondaries. The predictions of my models are compared with diagnostics of the mass accretion rate in CVs and it is found that results are intermediate between the saturated and the older braking prescription. Taken together these suggest that either the angular momentum loss rate may be higher in CV secondaries than in single stars of the same rotation period, or that accretion happens in duty cycles. Possible origins of the Period Gap are discussed. It is demonstrated that main-sequence mergers can (open full item for complete abstract)

Committee: Marc Pinsonneault (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2005, Astronomy

We investigate the calibration and application of reverberation mapping techniques for determining black hole (BH)masses in active galactic nuclei (AGNs). We present revised BH mass determinations for several AGNs based on the use of updated methodologies with archival data, demonstrating significant reductions in the sizes of the BH mass uncertainties. Moreover, the study of the Seyfert 1 galaxy, NGC 3783, shows that the gas in the broad-line region of this AGN obeys the virial theorem. We use measurements of stellar velocity dispersions, σ*, in AGNs and the assumption that AGNs follow the same relation between BH mass and σ* as quiescent galaxies to provide the first empirical calibration for reverberation-based BH masses. We also attempt to determine an independent calibration of these masses by studying the reverberation-mapped AGN, NGC 4151, with ground- and space-based observations, and by trying to constrain the BH mass through modeling of the galaxy's stellar dynamics. We estimate the BH masses and bolometric luminosities in ~400 AGNs selected from the multi-wavelength AGN and Galaxy Evolution Survey (AGES), where the BH masses are calculated from scaling relationships that have grown out of reverberation mapping. We find the distribution of Eddington ratios at fixed luminosity to be sharply peaked around value of 1/3, with a dispersion of just 0.3 dex. The distribution of Eddington ratios at fixed mass looks to be similarly narrow, and we are able to confirm a drop in the underlying distribution at low Eddington ratios for certain combinations of redshift and BH mass – all previous studies in these redshift-mass bins are affected by selection effects at low Eddington ratio (as are the AGES data in lower mass or higher redshift bins). The dominance of AGN accretion at rates relatively close to the Eddington limit has important implications for the growth of BHs and the joint evolution of BHs and their host galaxies.

Committee: Bradley Peterson (Advisor) Subjects: Physics, Astronomy and Astrophysics

Doctor of Philosophy, The Ohio State University, 2005, Astronomy

The bias of galaxies with respect to the underlying matter distribution has long been an obstacle to constraining cosmology from measurements of galaxy clustering. Recent advancements in quantifying bias have made it possible to model galaxy clustering from linear to strongly non-linear scales, creating unique methods through which to constrain cosmological parameters that are complementary to more standard, large-scale techniques. These advances are encapsulated in the Halo Occupation Distribution (HOD), in which the bias of galaxies is described at the level of individual dark matter halos. For a given cosmological model, the parameters that specify the number of galaxies that reside in each halo can be constrained by measurements of the galaxy correlation function. With these HOD parameters, the given cosmology model can be tested through a number of other clustering measures that are more sensitive to the underlying dark matter distribution. The clustering measures I investigate in this thesis are mass-to-light ratios, redshift-space distortions, and galaxy void statistics. Mass-to-light ratios of galaxy clusters are uniquely suited to the halo occupation approach because the HOD can specify the number of galaxies in a halo as a function of luminosity. Galaxy bias directly influences the amount of light per unit mass in a cosmological model. I combine HOD models with observational measurements of cluster M/L ratios to test varying cosmologies. Using the HOD to model galaxy clustering in redshift-space allows one to combine data from small and large scales to break the degeneracies that govern the application of models based on linear theory alone. I use numerical simulations to calibrate a new analytic model and apply this model to observations of the redshift-space correlation function from the Sloan Digital Sky Survey. Galaxy voids prove to be insensitive to the details of halo occupation or the cosmological model assumed. This makes void statistics a sensitiv (open full item for complete abstract)

Committee: David Weinberg (Advisor) Subjects: Physics, Astronomy and Astrophysics