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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

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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

1D stellar evolution and nucleosynthesis simulations have traditionally modeled the mixing within convection zones as a diffusive process. The fluids within a convection zone are advecting and do not diffuse. However the diffusive approximation is valid when the burning timescale of an exothermic reaction is longer than the convective turn over timescale to which the mixing of those species is approximated over. Since it is 1D, it also assumes that the material is isotropically distributed within the convection zone. In the He-flash convection zones of rapidly accreting white dwarfs (RAWD) H is ingested and burned well within the convective turn over time of 38 minutes. The H is burned through the exothermic 12C(p,γ)13N reac- tion, Q = 1.944 MeV, and then the unstable 13N, with a half-life of 9.6 minutes, will decay to 13C which will undergo the 13C(α,n)16O reaction releasing neutrons. The neutron densities, depending on the H-ingestion rates and mixing details, reach Nn ≈ 1013 − 1015 cm−3 which starts the i-process within the convection zone. The H burning provides energy to the flow leading to the dynamic details of the flow being important for the mixing of the H and thus the i-process nucleosynthesis. This is a convective-reactive environment. The isotropic, well mixed over many convective turn over timescales, and long burning timescale assumptions for H in the diffusive approximation are broken in the convective-reactive environment of a He-shell flash convection zone in a RAWD. To more accurately model convective-reactive mixing environments, a 1D two stream advective mixing model is formulated. A downstream advects H-rich material from the top of the convection zone down to the H-burning region while the upstream advects H-poor material back up to the upper convective boundary. The mixing model includes a horizontal mass flux, γ, which describes the efficiency to which mass is mixed between the two streams. This predominately causes the homogenization of the material between the two streams. The radial mass flux, α, and the horizontal mass flux, γ, are calibrated from 3D hydrodynamic simulations of the RAWD in order to model the mixing within the He-flash shell convection zone. The downsampled 3D cartesian data output, the briquette data, from the 3D hy- drodynamic simulations is used to compute γ. This required using numerical tools to interpolate quantities onto spherical shells from 3D cartesian data and to decompose the radial velocity field into its spherical harmonic modes. Trilinear interpolation is the simplest 3D interpolation method that was tested and it was the interpolation method of choice due to the constraints it has on the interpolating function. The validity of using higher order methods on the briquette data was studied in detail but was determined to not be usable due to the computational effort and constraints of the methods. The two stream model post-processing of the H burning within the 3D hydro- dynamic simulations of the RAWD showed excellent agreement in the metrics of the total mass of H burned, the burning rate and burning location of H. This includes two models which undergo dramatic H-ingestion and burning events caused by a GOSH, Global Oscillations of Shell H-ingestion. By adding a network containing 1000’s of species to the 1D advective mixing model, the i-process from the RAWD is simulated and compared with a traditional 1D diffusive mixing model. The resulting neutron densities between the two models are comparable however the efficiency to which each produce the heaviest stable elements are different. To reproduce the elemental abun- dance distribution of the CEMP-r/s star CS31062-050, the diffusive model is run for 15 days of stellar time while the advective model is run for 20 days. The H-ingestion into the He-shell as predicted by the stellar evolution calculations lasts 30 days. The i-process material within the RAWD can be removed from it and participate in the galactic chemical evolution of the galaxy that it resides in. This is due to the RAWD possibly reaching the Chandrasekhar mass and from the loss of material through stellar winds and common envelope interactions with its nearby companion star. / Graduate

White dwarfs are among the most common objects in the stellar halo; however, due to their low luminosity and low number density compared to the stars in the discs of the Milky Way, they are scarce in the observable volume. Hence, they are still poorly understood one hundred years after their discovery as relatively few have been observed. They are crucial to the understanding of several fundamental properties of the Galaxy – the geometry, kinematics and star formation history, as well as to the study of the end-stage of stellar evolution for low- and intermediate-mass stars. White dwarfs were traditionally identified by their ultraviolet (UV) excess, however, if they have cooled for a long time, they become so faint in that part of the spectrum that they cannot be seen by the most sensitive modern detectors. Proper motion was then used as a means to identify white dwarf candidates, due to their relatively large space motions compared to other objects with the same colour. The use of proper motion as a selection criterion has proven effective and has yielded large samples of candidates with the SuperCOSMOS Sky Survey and Sloan Digital Sky Survey. In this work I will further increase the sample size with the Panchromatic Synoptic Telescope And Rapid Response System 1 (Pan–STARRS1). To construct luminosity functions for the study of the local white dwarfs, I require a density estimator that is generalised for a proper motion-limited sample. My simulations show that past works have underestimated the density when the tangential velocity was assumed to be a constant intrinsic parameter of an object. The intrinsically faint objects which are close to the upper proper motion limits of the surveys are most severely affected because of the poor approximation of a fixed tangential velocity. The survey volume is maximised by considering the small/intermediate scale variations in the observation properties at different epochs. This type of volume maximisation has not been conducted before because previous surveys did not have multi-epoch data over a footprint area of this size. The tessellation of the 3π Steradian Survey footprint is so complex that the variations are strong functions of position. I continue to demonstrate how a combination of a galactic model and the photometric limits as a function of position can give a good estimate of the completeness limits at different colour and different line-of-sight directions. Finally, I compare the derived white dwarf luminosity function with previous observational and theoretical work. The effect of interstellar reddening on the luminosity functions is also investigated.

As the endpoints of stars less massive than roughly eight solar masses, the population of Galactic white dwarfs (WD) contain information about complex stellar evolution processes. Associated pairs of WDs add an extra degree of leverage; both WDs must have formed and evolved together. The work presented in this dissertation uses various populations of double WDs (DWD) to constrain evolution of both single and binary stars. One example is the set of low-mass WDs with unseen WD companions, which are formed through a dynamically-unstable mass loss process called the common envelope. To work toward a quantitative understanding of the common envelope, we develop and apply a Bayesian statistical technique to identify the masses of the unseen WD companions. We provide results which can be compared to evolutionary models and hence a deeper understanding of how binary stars evolve through a common envelope. The statistical technique we develop can be applied to any population of single-line spectroscopic binaries. Binaries widely separated enough that they avoid any significant interaction independently evolve into separate WDs that can be identified in photometric and astrometric surveys. We discuss techniques for finding these objects, known as wide DWDs. We present a catalog of 142 candidate wide DWDs, combining both previously detected systems and systems we identify in our searches in the Sloan Digital Sky Survey. Having been born at the same time, the masses and cooling ages of the WDs in wide DWDs, obtained with our spectroscopic follow-up campaign can be used to constrain the initial-final mass relation, which relates a main sequence star to the mass of the WD into which it will evolve. We develop a novel Bayesian technique to interpret our data and present our resulting constraints on this relation which are particularly strong for initial masses between two and four solar masses. During this process, we identified one wide DWD, HS 2220+2146, that was peculiar since the more massive WD in this system evolved second. We construct an evolutionary formation scenario in which the system began as a hierarchical triple in which the inner binary merged (possibly due to Kozai-Lidov oscillations) forming a post-blue straggler binary. The system then evolved into the DWD we observe today. We further discuss the potential for identifying more wide DWDs, including peculiar systems like HS 2220+2146, in future surveys such as Gaia.

This dissertation uses radio observations with the Karl G. Jansky Very Large Array (VLA) to investigate the mechanisms that power and shape accreting white dwarfs (WD) and their ejecta. We test the predictions of both simple spherical and steady-state radio emission models by examining nova V1723 Aql, nova V5589 Sgr, symbiotic CH Cyg, and two small surveys of symbiotic binaries. First, we highlight classical nova V1723 Aql with three years of radio observations alongside optical and X-ray observations. We use these observations to show that multiple outflows from the system collided to create early non-thermal shocks with a brightness temperature of ⪆10⁶ K. While the late-time radio light curve is roughly consistent an expanding thermal shell of mass 2x10⁻⁴ M ⊙ solar masses, resolved images of V1723 Aql show elongated material that apparently rotates its major axis over the course of 15 months, much like what is seen in gamma-ray producing nova V959 Mon, suggesting similar structures in the two systems. Next, we examine nova V5589 Sgr, where we find that the early radio emission is dominated by a shock-powered non-thermal flare that produces strong (kTₓ > 33 keV) X-rays. We additionally find roughly 10⁻⁵ M⊙ solar masses of thermal bremsstrahlung emitting material, all at a distance of ~4 kpc. The similarities in the evolution of both V1723 Aql and V5589 Sgr to that of nova V959 Mon suggest that these systems may all have dense equatorial tori shaping faster flows at their poles. Turning our focus to symbiotic binaries, we first use our radio observations of CH Cyg to link the ejection of a collimated jet to a change of state in the accretion disk. We additionally estimate the amount of mass ejected during this period (10⁻⁷ M⊙ masses), and improve measurements of the period of jet precession (P=12013 +/- 74 days). We then use our survey of eleven accretion-driven symbiotic systems to determine that the radio brightness of a symbiotic system could potentially be used as an indicator of whether a symbiotic is powered predominantly by shell burning on the surface of the WD or by accretion. We additionally make the first ever radio detections of seven of the targets in our survey. Our survey of seventeen radio bright symbiotics, comparing observations before and after the upgrades to the VLA, shows the technological feasibility to resolve the nebulae of nearby symbiotic binaries, opening the door for new lines of research. We spatially resolve extended structure in several symbiotic systems in radio for the first time. Additionally, our observations reveal extreme radio variability in symbiotic BF Cyg before and after the production of a jet from the system. Our results from our surveys of symbiotics provide some support for the model of radio emission where the red giant wind is photoionized by the WD, and suggests that there may be a greater population of radio faint, accretion driven symbiotic systems. This work emphasizes the powerful nature of radio observations as a tool for understanding eruptive WD binaries and their outflows.

Wong Ka Wah = 奇異星的特性 / 黃嘉華. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 98-101). / Text in English; abstracts in English and Chinese. / Wong Ka Wah = Qi yi xing de te xing / Huang Jiahua. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- History of Compact Stars --- p.1 / Chapter 1.2 --- The Proposal of Strange Quark Stars --- p.2 / Chapter 1.3 --- Outline of the Thesis --- p.3 / Chapter 2 --- Cold Equation of State from Perturbative QCD --- p.6 / Chapter 2.1 --- Description of Strange Quark Matter --- p.7 / Chapter 2.2 --- MIT Bag Model --- p.8 / Chapter 2.3 --- Perturbative QCD --- p.10 / Chapter 2.4 --- Comparison with MIT Bag Model --- p.11 / Chapter 3 --- Static Structure of Strange Stars --- p.16 / Chapter 3.1 --- Static Equilibrium --- p.16 / Chapter 3.2 --- Models --- p.18 / Chapter 3.3 --- Results of Global Properties and Discussions --- p.18 / Chapter 4 --- Stability of Strange Quark Matter --- p.25 / Chapter 4.1 --- Absolute Stable Condition --- p.25 / Chapter 4.2 --- Weak Stable Condition --- p.26 / Chapter 4.3 --- Stability Condition Compared to Neutron Stars --- p.27 / Chapter 4.4 --- Conclusion --- p.28 / Chapter 5 --- Effect of Massive Strange Quarks --- p.31 / Chapter 5.1 --- Numerical Analysis of the Effect of Strange Quark Mass on the EOS --- p.33 / Chapter 5.2 --- Structure of Strange Stars with Strange Quark Mass --- p.37 / Chapter 5.3 --- Conclusion --- p.38 / Chapter 6 --- QCD Phase Transition in a Compact Star --- p.46 / Chapter 6.1 --- Cooling Properties --- p.47 / Chapter 6.1.1 --- Heat capacity of quark stars --- p.49 / Chapter 6.1.2 --- Luminosity of quark stars --- p.50 / Chapter 6.1.3 --- Microphysics of the neutron star cooling --- p.54 / Chapter 6.2 --- Handling of the Phase Transition --- p.56 / Chapter 6.3 --- The Models --- p.59 / Chapter 6.4 --- Results --- p.60 / Chapter 6.4.1 --- Method 1 --- p.61 / Chapter 6.4.2 --- Method 2 --- p.66 / Chapter 6.5 --- Discussion and Conclusion --- p.66 / Chapter 7 --- Formation of a Strange Star --- p.73 / Chapter 7.1 --- Formalism of the Problem --- p.73 / Chapter 7.2 --- Lagrangian Hydrodynamics --- p.74 / Chapter 7.3 --- Hot Equation of State --- p.75 / Chapter 7.3.1 --- Nuclear Matter EOS --- p.75 / Chapter 7.3.2 --- Quark Matter EOS --- p.77 / Chapter 7.3.3 --- Mixed Phase --- p.78 / Chapter 7.4 --- Initial Models --- p.78 / Chapter 7.5 --- Results --- p.80 / Chapter 7.6 --- Discussion and Conclusion --- p.81 / Chapter 8 --- Conclusion --- p.95 / Bibliography --- p.98 / Chapter A --- Solving the EOS --- p.102 / Chapter B --- Solving C from Eq. (7.10) --- p.105