A Study on the Evolution of Compact Star Binaries and Stellar X-ray Sources
Abstract
X-ray serves as one of the most important domains of discovery in astronomy. It could be used to study the properties as well as the formation and evolution of X-ray emitting objects. X-ray can also be used to constrain the formation and evolution history of galaxies in the universe.
In this thesis, we discuss the properties of the X-ray point sources, especially those with white dwarfs as accretors. We focus on the evolution of these binaries and their progenitors, as well as the relation between these objects and their host environments with the numerical and observational methods. We further put constraints on the final product and the possible connection to the type Ia supernovae. Our main results are as follows: (1) We study the case in which the thermally unstable accretion disks occur in binaries, and apply to the evolution of GRO J1744-28 and type Ia supernovae. Our result shows that GRO J1744-28 could have evolved from a binary composed by a normal star and an ONeMg white dwarf and with the white dwarf as the accretor. During its evolution, the white dwarf experienced accretion from the X-ray irradiated unstable accretion disk, then accumulated mass by burning the accreted matter on its surface before it collapsed to a neutron star. The new formed neutron star then accreted from the companion again, and evolved to its present properties. We also apply the unstable disks to the binaries with C/O white dwarfs as accretors, and calculate the region of the initial companion masses and orbital periods which could lead to successful type Ia supernovae. The results suggest that the companion star of the progenitor system could have the initial mass as low as ≲ 1.5 M_{⊙}. (2) We study the λ parameter in the common envelope evolution. Our results show that the λ parameter varies for the stars with different initial masses. For the same star, λ also varies in different evolutional stages. At the end of their evolution, the stars with the approximate initial mass between 3-6 M_{⊙} could have λ as large as several hundreds. On the other hand, given similar initial mass and evolutional stage, Pop. I stars always have higher λ than Pop. II stars. (3) We study the statistical properties of the faint X-ray point sources in the Galactic bulge and globular clusters. Our results show that there is a consistency between the luminosity function of the point sources in the Galactic bulge and that in the local field. We confirm the flatness of the luminosity functions in the globular clusters. The globular clusters seem to harbor more luminous X-ray sources and less fainter ones. Our study gives quantitative correlation between the slope of the luminosity functions and the specific dynamical encounter rates. Further investigation shows that the source number density is also related to the location of the source in the cluster, and the initial binary fraction of clusters.- Publication:
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Acta Astronomica Sinica
- Pub Date:
- March 2014
- Bibcode:
- 2014AcASn..55..191X
- Keywords:
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- binaries: general;
- stars: evolution;
- Â supernovae: general;
- X-rays: binaries;
- novae;
- cataclysmic variables