| 其他摘要 | White dwarfs are stellar cores left over from the late evolution of middle and small mass (0.8 𝑀⊙ < 𝑀 < 7 𝑀⊙) stars, which represent the ultimate fate of more than 95% of the celestial objects in the universe. White dwarfs contain a lot of information about stars from birth to death. A single white dwarf can be used to verify the evolution theory of stars, including the material loss rate in the post AGB stage at the end of the evolution, which also directly affects the star's initial-to-final mass relation. White dwarfs are also possible results of the evolution of multiple star systems. It is estimated that 25% ∼ 30% of white dwarfs are the results of the evolution after merging, and white dwarfs with mass less than 0.4𝑀⊙ that have been found are generally considered as the results of the evolution of binary stars. Therefore, white dwarfs can also be used to verify the correctness of the theory of binary stars evolution. The compact degenerate core of white dwarf represents an ideal laboratory of theoretical physics under extreme conditions. The research on the cooling sequence and cooling model of white dwarf makes it possible to use the white dwarf as an independent age and distance indicator for various star populations, and provides an independent cosmic clock to limit the ages of stars in each star population in the Milky Way. Through the study of white dwarf populations, we can invert the important characteristics of galaxy evolution such as star formation rate of the Milky Way. The study of the properties of the white dwarf populations needs to integrate the spatial density, luminosity function and other information of the white dwarf, and the acquisition of these information needs a large number of uniform and well-defined white dwarf samples. In the early days, due to the limitation of observation instruments, the spectral identification of white dwarfs was inefficient. In the past two decades, the development of large-scale sky surveys, such as GALEX (Galaxy Evolution Explorer), SDSS (The Sloan Digital Sky Survey), GAIA (Global Astronomic Interferometer for Astrophysics), LAMOST (Large Sky Area Multi Object Fiber Spectroscope Telescope), has greatly increased the number of astrophysical information acquisition, such as photometry and spectrum, and the search for white dwarf has made great progress. Here we use the low resolution spectral data of LAMOST's eighth data release (DR8), combined with GAIA's high-precision photometry and parallax data, to identify white dwarfs. According to the characteristic spectral lines of the white dwarf spectrum and the larger broadening of the spectral lines, we have identified a total of 4692 white dwarf systems and 85 cataclysmic variable star systems in LAMOST DR8. After comparison, the completeness of the white dwarf sample is 80%, and the classification accuracy is 99%, so our identification is very accurate. The final LAMOST white dwarfs sample can well reflect the distribution of different types of white dwarf in the GAIA H-R diagram. |
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