paper

Hot Subdwarf Stars Identified in Gaia DR2 with Spectra of LAMOST DR6 and DR7. II. Kinematics

arXiv:2006.01655 · doi:10.3847/1538-4357/ab98f3

Abstract

Combining the LAMOST radial velocities with Gaia parallaxes and proper motions, we presented 3D Galactic space motions and the orbits of 182 single-lined hot subdwarf stars. These stars have been identified by Lei et al. (2020) in Gaia DR2 with LAMOST DR6 and DR7 spectra. He-rich hot subdwarf stars with log(y)>0 show the largest standard deviations of the Galactic velocity components and orbital parameters, while those with -1<log(y)<0 exhibit the second largest standard deviations. The two groups of He-deficient stars with log(y)<-1 show similar standard deviations, which is systematically lower compared to He-rich stars. We also presented a kinematic population classification of the four hot subdwarf helium groups based on their positions in the U-V velocity diagram, J_z-eccentricity diagram and their Galactic orbits. The overall tendency of the fractional distributions of the four hot subdwarf helium groups in the halo, thin disk and thick disk is largely consistent with the findings reported by Luo et al.(2019) based on LAMOST DR5, which appears to support the predictions of binary population synthesis (Han et al. 2003; 2008). He-deficient stars with -2.2<log(y)<-1 likely origin from stable the Roche lobe overflow channel, He-deficient stars with log(y)<-2.2 from the common envelope ejection channel, and He-rich stars with log(y)>0 from the merger channel of double He white dwarf stars. The fraction of He-rich hot subdwarf stars with -1<log(y)<0 in the thin disk and the halo are far higher than in the thick disk, which implies that these stars have different formation channels in the thin disk and in the halo.

15 pages, 6 figures, accepted for publication in APJ. arXiv admin note: substantial text overlap with arXiv:1906.09393

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