Peculiar stars are a key of understanding stellar physics, which can help us to check and to improve stellar evolution and dynamic theories. In this paper, we searched for two types peculiar stars: symbiotic stars and hypervelocity stars.(1) Symbiotic stars are interacting binary systems with the longest orbital periods. They typically consist of a white dwarf (WD) and a red giant that are embedded in a nebula. These objects are natural astrophysical laboratories for studying the evolution of binaries. Based on activity of the WD, symbiotic stars are classified into Z And-like symbiotic stars and symbiotic novae. They also can be divided into S-, D-, D′-, and S+IR-type according to their giant companions. In addition, D′-type and a few of S-type symbiotic stars are called as yellow symbiotic stars due to their cool giant companions with Teff > 4000 K. Current estimates of the population of symbiotic stars in the Milky Way is about 3 x 105. However, a current census has found 255. The LAMOST survey can obtain hundreds of thousands of stellar spectra per year, providing a good opportunity to search for new symbiotic stars. We detect four such binaries among 4,147,802 spectra released by LAMOST, of which two are new identifications. The first is LAMOST J12280490–014825.7, considered to be a yellow symbiotic star. The second is LAMOST J202629.80+423652.0, a D-type symbiotic star.(2) Hypervelocity stars (HVSs) are stars which can escape the Milky Way. They are important tools for probing the Galactic structure and help us to improve the stellar evolution and dynamic theories. Several dozen HVS candidates have been reported based on the second data release of Gaia (Gaia DR2). However, it has been proven that the radial velocities of some Gaia HVS candidates are not reliable. In this dissertation, we employ refined astrometric criteria to re-examine Gaia DR2, obtained a sampleof HVS and high velocity star candidates more reliable than those found by previous studies. We develop a method called Binary Escape Probability Analysis to identify some HVS candidates. The method allows us to work with stars having only 2 epochs of measured radial velocities. These stars were usually discarded in previous similar studies. A scrutiny of our final results sheds light on selection effects present in our studies, which we propose to be the focus of future studies. In total, we find 3 HVS and 21 high velocity star candidates, 3 and 11 of which are new, respectively. Judging by their historical trajectories, which we calculate, all 3 HVS candidates could not have had Galactic center origins. Further monitoring is required to confirm their status.
修改评论