大样本恒星演化研究组知识库

Based on the Gaia DR2 catalog of hot subdwarf star candidates, we identified 1587 hot subdwarf stars with spectra in LAMOST DR7. We present atmospheric parameters for these stars by fitting the LAMOST spectra with Tlusty/Synspec non-LTE synthetic spectra. Combining LAMOST radial velocities and Gaia Early Data Release 3 (EDR3) parallaxes and proper motions, we also present the Galactic space positions, velocity vectors, orbital parameters and the Galactic population memberships of the stars. With our He classification scheme, we identify four groups of He rich hot subdwarf stars in the T (eff) - log g and T (eff) - log(nHe/nH) diagrams. We find two extreme He-rich groups (eHe-1 and eHe-2) for stars with log(nHe/nH) >= 0 and two intermediate He-rich groups (iHe-1 and iHe-2) for stars with -1 <= log(nHe/nH) < 0. We also find that over half of the stars in Group eHe-1 are thick-disk stars, while over half of the stars in Group eHe-2 correspond to thin-disk stars. The disk population fractions of Group iHe-1 are between those of Group eHe-1 and eHe-2. Almost all of the stars in Group iHe-2 belong to the thin disk. These differences indicate that the four groups probably have very different origins. Comparisons between hot subdwarf stars in the halo and in the Galactic globular cluster omega Cen show that only He-deficient stars with -2.2 <= log(nHe/nH) < -1 have similar fractions. Hot subdwarfs with log(nHe/nH) >= 0 in omega Cen have no counterparts in the thick-disk and halo populations, but they appear in the thin disk.