No description available.

No description available.

A new type of astronomical polarimeter is presented that incorporates a fused silica stress-birefringent modulator which simultaneously allows the selection of chopping frequency (≤ 5 Hz) and spectral tuning (1 ≤ λ ≤ 2.5 μm) with very high modulation efficiency. Two integrating detector packages are discussed. The first uses a single germanium photodiode and HR polaroid analyzer and achieves σᵥ = 1% for a J = 14.5 object in 0.5 hr with the MMT. The second package uses a 12 x 30 pixel HgCdTe array and MgF₂ Wollaston prism to provide four simultaneous polarimetric channels that properly eliminate the systematic errors resulting from "staring" mode operation. The instrumental polarizations of the MMT are calculated using Mueller calculus and experimentally verified. It is found that the hexagonal symmetry of the telescope cancels the large amplitude spurious polarizations that arise from the single "arms" and results in a polarimetric efficiency term that is a function only of spectral bandpass and not sky position. Therefore, the MMT behaves essentially like a clean Cassegrain telescope. The continuum polarizations of five isolated highly magnetic white dwarfs are investigated both observationally and theoretically. The most complete broad-band polarimetric survey throughout the spectral region 0.35 ≤ λ ≤ 1.65 μm is performed. An apparent correlation in the linear polarizations of Grw + 70°8247, GD229, and G240-72 is discovered. In addition, no evidence for time-dependent rotation of position angle is found for any of the stars. Hydrogen Balmer photoionization occurring from the magnetically-perturbed bound states into the Coulomb-Lorentz mixed quasi-Landau continuum is investigated with the aid of recent high field calculations. Finally, the continuum polarization of Grw + 70°8247 is compared to models for cyclotron and inverse magnetobremsstrahlung absorptions in a dipolar field. The conclusion is that the continuum polarizations of these objects still eludes an exact description. New observations of BG C Mi reveal the first definitive discovery of polarized cyclotron emission in any intermediate polar and confirms that the long-held basic model of a magnetically accreting white dwarf is correct. The wavelength dependence of circular polarization is found to increase rapidly into the near-infrared, from V(I) = -0.25±0.06% to V(J) = -1.74±0.26% and suggests a field strength in the cyclotron emission region near 5-10 MG if the system scales directly with the AM Her stars.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 188-196). Available also in a digital version from Dissertation Abstracts.

No description available.

No description available.

Wong, Ka Wing = 含有暗物質核心的白矮星的物理性質 / 黃家榮. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 81-86). / Abstracts in English and Chinese. / Wong, Ka Wing = Han you an wu zhi he xin de bai ai xing de wu li xing zhi / Huang Jiarong. / Abstract --- p.ii / Acknowledgement --- p.iv / List of Abbreviations --- p.v / List of Figures --- p.vi / Table of Contents --- p.xi / Chapter 0 --- Introduction --- p.1 / Chapter 1 --- White Dwarfs --- p.5 / Chapter 1.1 --- Introduction --- p.5 / Chapter 1.2 --- Observation --- p.6 / Chapter 1.3 --- Mass-Radius Relationship & Mass Limit --- p.9 / Chapter 1.4 --- Type Ia Supernovae --- p.14 / Chapter 2 --- Dark Matter --- p.16 / Chapter 2.1 --- Introduction --- p.16 / Chapter 2.2 --- Observational Evidences --- p.17 / Chapter 2.3 --- Dark Matter Candidates and their Categorization --- p.21 / Chapter 3 --- Moon-sized White Dwarf with a Dark Matter Core --- p.26 / Chapter 3.1 --- Introduction --- p.26 / Chapter 3.2 --- Model --- p.29 / Chapter 3.3 --- Results --- p.32 / Chapter 3.3.1 --- Typical Density Profile --- p.32 / Chapter 3.3.2 --- M-R Curves --- p.33 / Chapter 3.3.3 --- Scaling in n --- p.35 / Chapter 3.3.4 --- BPS Equation of State --- p.40 / Chapter 3.4 --- Discussion --- p.41 / Chapter 4 --- Newtonian Hydrodynamic Simulation of a Spherically Symmetric Star --- p.44 / Chapter 4.1 --- Introduction --- p.44 / Chapter 4.2 --- WENO Scheme --- p.46 / Chapter 4.3 --- Runge-Kutta Time Discretization --- p.48 / Chapter 4.4 --- Fluid Dynamics without Gravity in One Dimension --- p.49 / Chapter 4.4.1 --- Riemann Problem Tests --- p.50 / Chapter 4.5 --- Spherically Symmetric Fluid Dynamics without Gravity --- p.54 / Chapter 4.5.1 --- Diffusion Problem --- p.55 / Chapter 4.6 --- Spherically Symmetric Star --- p.57 / Chapter 4.6.1 --- Radial Oscillation of a White Dwarf --- p.58 / Chapter 4.6.2 --- Radial Oscillation of a White Dwarf with a Point-Sized Dark Matter Core --- p.64 / Chapter 4.7 --- Discussion --- p.68 / Chapter 5 --- Newtonian Hydrodynamic Simulation of a Spherically Symmetric Two-Fluid Star --- p.69 / Chapter 5.1 --- Introduction --- p.69 / Chapter 5.2 --- Spherically Symmetric Two-Fluid Stars --- p.70 / Chapter 5.2.1 --- A White Dwarf with a Dark Matter Core --- p.71 / Chapter 5.3 --- Discussion --- p.77 / Chapter 6 --- Summary --- p.79 / Bibliography --- p.81

Not available / text

We present updated observations of a pilot survey of 14 pulsating DA white dwarfs, monitored for evidence of center-of-mass motion caused by a planetary companion. We have nearly doubled the number of periodicites for which we can produce O-C diagrams that document pulse arrival times from our stars, and have implemented a method to minimize the apertures we use in our reductions in order to reduce sky noise. In addition to a previously published candidate, GD66, we have identi fed at least four more systems worthy of rigorous observational follow-up. We have also implemented a method, a generalized Lomb-Scargle periodogram, that takes into account weighted points in order to characterize any periodic behavior present in our O-C diagrams. For at least one DAV within this same sample, we have found strong observational evidence for an evolutionary time scale (via the rate of period change) that is inconsistent with cooling alone. In that star, WD0111+0018, we report for the first time measurement of the rate of period change of nonlinear combination frequencies in a pulsating white dwarf. We speculate that this may be caused by a changing rotation rate that aff ects only modes with m not equal to 0. / text