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arXiv 2107.09302astro-ph.SRastro-ph.GA
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热亚矮星大气参数、动力学和起源--基于盖亚DR2和LAMOST DR7观测的1587颗热亚矮星

Hot subdwarf Atmospheric parameters, Kinematics, and Origins -- Based on 1587 hot subdwarf stars observed in Gaia DR2 and LAMOST DR7

Yangping Luo, Peter Nemeth, Kun Wang, Xi Wang, Zhanwen Han

摘要:

基于盖亚DR 2目录的热亚矮星候选者,我们确定了1587热亚矮星的光谱在LAMOST DR 7。我们提出了这些恒星的大气参数,通过拟合LAMOST光谱与{ \sc Tlusty/Synspec}非LTE合成光谱。结合LAMOST径向速度和盖亚早期数据发布3(EDR 3)的弛豫和自行,我们还提出了银河系的空间位置,速度矢量,轨道参数和银河系人口成员的恒星。利用我们的He分类方案,我们在$T_{\rm eff}-\log\,g$和$T_{\rm eff}-\log{(n{\rm He}/n{\rm H})}$图中识别出四组富He热亚矮星。我们发现两个极端的富氦族($e$ He-1和$e$ He-2)的恒星与$\log{(n{\rm He}/n{\rm H})}\geq0$和两个中间富氦族($i$ He-1和$i$ He-2)的恒星与$-1\le\log{(n{\rm He}/n{\rm H})}<0$。我们还发现,在$e$ He-1中,超过一半的恒星是厚盘星,而在$e$ He-2中,超过一半的恒星对应于薄盘星。组$i$ He-1的盘群体分数介于组$e$ He-1和$e$ He-2的盘群体分数之间。几乎所有的$i$ He-2恒星都属于薄盘。这些差异表明,这四个群体可能有非常不同的起源。在晕中的热亚矮星和银河球状星团$ω$ Cen中的热亚矮星之间的比较表明,只有$-2.2\le\log{(n{\rm He}/n{\rm H})}<-1$中的氦缺乏恒星具有相似的分数。在$ω$ Cen中含有$\log{(n{\rm He}/n{\rm H})}\ge 0$的热次矮星在厚盘和晕中没有对应物,但它们出现在薄盘中。

英文摘要:

Based on the Gaia DR2 catalogue 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 {\sc 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 $T_{\rm eff}-\log\,g$ and $T_{\rm eff}-\log{(n{\rm He}/n{\rm H})}$ diagrams. We find two extreme He-rich groups ($e$He-1 and $e$He-2) for stars with $\log{(n{\rm He}/n{\rm H})}\geq0$ and two intermediate He-rich groups ($i$He-1 and $i$He-2) for stars with $-1\le\log{(n{\rm He}/n{\rm H})}<0$. We also find that over half of the stars in Group $e$He-1 are thick disk stars, while over half of the stars in Group $e$He-2 correspond to thin disk stars. The disk population fractions of Group $i$He-1 are between those of Group $e$He-1 and $e$He-2. Almost all stars in Group $i$He-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 $ω$ Cen show that only He-deficient stars with $-2.2\le\log{(n{\rm He}/n{\rm H})}<-1$ have similar fractions. Hot subdwarfs with $\log{(n{\rm He}/n{\rm H})}\ge 0$ in $ω$ Cen have no counterparts in the thick disk and halo populations, but they appear in the thin disk.

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