Evolution Of Low-mass X-ray Binaries

This thesis explores influence of compact star mass on the evolution of low-mass X-ray binaries(LMXBs), including the following three directions:First, change of bifur-cation period of binary system with initial accretor mass change from1.4to1000M(?) Second, with fixed initial companion star mass(l M(?))and initial orbit period(P,=2d) while different initial accreting star mass, the evolution of LMXBs system; Third, whether the final Porh—A/WD relation of the binary system is sensitive to initial accret-ing star mass.The structure of this thesis is as follows. We first present a review on observations and theories of X-ray binaries in Chapter1, including observational characteristics of Galaxy X-ray sources, formation and evolution of LMXBs and some corresponding physical mechanism during these processes.In chapter2, we present our results of numerical calculations on the evolution of the chosen low-mass X-ray binary systems. For the accreting compact object we consider the initial mass of1.4,10,20,100,200,500and1000M(?), corresponding to neutron stars(NSs), stellar-mass and intermediate-mass black holes(BHs), respectively. Mass transfer in these binaries is driven by nuclear evolution of the donors and/or orbital an-gular momentum loss due to magnetic braking and gravitational wave radiation. For the different systems, we determine their bifurcation periods Pbif that separate the forma-tion of converging systems from the diverging ones, and show that Pbif changes from-Id to≥3d for1M(?)donor star, with increasing initial accretor mass from1.4to1000M(?). This means that the dominant mechanism of orbital angular momentum loss changes from magnetic braking to gravitaional radiation. As an illustration we com-pare the evolution of binaries consisting of a secondary star of1M(?) at a fixed initial period of2d. In the case of the NS or stellar-mass BH accretor, the system evolves to a well-detached He WD-NS/BH pair, while it evolves to an ultra-compact binary if the compact object is an intermediate-mass BH. Thus the binary evolution heavily depends upon the mass of the compact object. However, we show that the final orbital period-white dwarf mass relation found for NS low-mass X-ray binaries is fairly insensitive to the initial mass of the accreting star, even if it is an intermediate-mass black hole.Finally, we summarize the above content and give the future direction of our work in Chapter3.