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

The absorption due to pairs of H₂ molecules is an important opacity source in the atmospheres of various types of planets and cool stars, such as late stars, low mass main sequence stars, brown dwarf stars, cool white dwarf stars, the ambers of the smaller, burnt out main sequence stars, exoplanets, etc., and therefore of special astronomical interest. Astronomers are interested in the outer planets as they still contain primordal matter. Furthermore, recent observations by the Hubble space telescope (in operation since 1990) have revealed several thousand cool white dwarf stars with temperatures of several thousand Kelvin. It is surprising that none of them has temperatures lower than roughly 4000 K. This means that the white dwarf stars have not had enough time to cool down to the temperature of the cosmic background radiation. Astrophysicists believe that this information can be used for an alternative and more accurate method of cosmochronology. However, the emission spectra of cool white dwarf stars differ significantly from the expected blackbody spectra of their cores, largely due to collision-induced absorption by collisional complexes of residual hydrogen and helium in the stellar atmospheres. In order to model the radiative processes in these atmospheres, which have temperatures of several thousand kelvin, one needs accurate knowledge of the induced dipole and potential energy surfaces of the absorbing collisional complexes, such as H₂--H₂, H₂--He, and H₂--H. These come from quantum-chemical calculations, which, for the high temperatures and high photon energies under consideration in this work, need to take into account that the H₂ bonds can be stretched or compressed far from equilibrium length. Since no laboratory measurements for these high temperatures and photon energies exist, one has to undertake \textit{ab initio} calculations which take into account the high vibrational and rotational excitation of the involved hydrogen molecules. However, before one attempts to proceed to higher temperatures and photon energies where no laboratory measurements exist it is good to check that the formalism is correct and reproduces the results at temperatures and photon energies where laboratory measurements exist, that is, at and below room temperature and for photon energies up to about 1.5 eV. In this work a formalism is developed to compute the binary collision-induced absorption of simple molecular complexes up to temperatures of thousands of kelvin and photon energies up to 2.5 eV, properly taking into account vibrational and rotational dependencies of the induced dipole and potential energy surfaces. In order to make the computational effort feasible, the isotropic potenial approximation is employed. The formalism is applied to collisional complexes of H₂--H₂, D₂--D₂, H₂--He, D₂--He, T₂--He, and H₂--H, and compared with existing laboratory measurements. / text

This dissertation is an observational exploration of the exciting physics that can be enabled by high-speed photometric monitoring of extremely low-mass (< 0.25 M[subscript sun symbol]) white dwarf stars, which are found in some of the most compact binaries known. It includes the cleanest indirect detection of gravitational waves at visible wavelengths, the discovery of pulsations in He-core WDs, the strongest evidence for excited p-mode pulsations in a WD, the discovery of the first tidally distorted WDs and their use to constrain the low-end of the WD mass-radius relationship, and the strongest cases of Doppler beaming observed in a binary system. It is the result of the more than 220 nights spent at McDonald Observatory doing high-speed photometry with the Argos instrument on the 2.1 m Otto Struve telescope, which has led to a number of additional exciting results, including the discovery of an intermediate timescale in the evolution of cooling DA WDs and the discovery of the most massive pulsating WD, which should have an ONe-core and should be highly crystallized. / text

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Study determined if 2MASS photometric data are reliable for luminosity classification using JHK plots of Reid and Hawley (2001). Effects of interstellar reddening on the placement of giant and dwarf data on the JIIK plot were analyzed. Dwarfs (N=54) were selected from Hipparchos and the 2MASS data reduced to an H-K range of 0.14-0.40. A disk dwarf region was identified using linear regression on the low space velocity stars. Giants selected from Volume 5 of the Michigan Catalogue of HD stars and SAG stars classified at Ball State University. They yielded 304 individual giants and 13 matches in the 0.14-0.40 H-K range respectively. The 2MASS data was reliable for luminosity classification of the SAGBSU giants. The classification of the Michigan giants was not possible due to interstellar reddening and the likely presence of faint giant companions. / Department of Physics and Astronomy

This paper presents the photometric luminosity classification of M dwarfs in Kaptyn’s Selected Area 124 (SA124). This project is part of an ongoing program at Ball State University to use R, I, and CaH photometry in an attempt to probe low luminosity star contributions to the luminosity function. Data is taken at the Southeastern Association for Research in Astronomy (SARA) telescope located at Kitt Peak, Arizona. With a limiting magnitude of R=15.0, we have observed ~75% of a full square degree in SA124 and have detected 19 M dwarf candidates, which are then confirmed using matched 2MASS J, H, and K magnitudes. We present the detections of 19 ±4.4 M dwarfs observed in SA124. The current estimates of our luminosity function are consistent with those previously determined for the galactic plane. / Department of Physics and Astronomy

This investigation in the 24 Kapteyn Selected Areas along the celestial equator examined 21 red dwarf stars identified in an objective-prism survey. These stars were classified as red dwarf stars using light at wavelengths between 5800 A and 6800 A. Using calcium-hydride-based luminosity classification, this study found 13 of these stars to be red giant stars, and only 6 stars were found to be red dwarfs. One star was determined to be warm star. One star was not clearly distinguishable as a dwarf or giant. Distance calculations for the red dwarf stars found that these stars lie within 40 parsecs of the sun. / Department of Physics and Astronomy

Red dwarf stars are one proposed solution to the dark matter problem in the Milky Way Galaxy These cool, low luminosity stars are difficult to detect and segregate in surveys. This study utilizes photometric data obtained on the Kron-Cousins photometric system to develop criteria that classifies stars as red. Two of the color indices are then used to create a two-color diagram to allow separation of giant and dwarf stars. An algorithm based on calculated equations is provided to separate the giant and dwarf stars after detection. A third class of stars, subdwarfs, is addressed as a potential problem in future surveys. Some suggestions for detecting and removing these contaminating stars from the data are offered. Finally, a colormagnitude diagram is developed for red dwarf stars with KronCousins photometry. This curve allows for fairly accurate determination of photometric parallaxes for the red dwarf stars.An attempt was made to segregate the red dwarfs into velocity classes prior to calibrating the color-magnitude diagram. It was found that this approach offered no additional useful information. / Department of Physics and Astronomy