标题： 利用LAMOST DR4 M巨星与Gaia DR2探测人马座星流 显示英文标题

标题： Detecting the Sagittarius stream with LAMOST DR4 M giants \& Gaia DR2

摘要： 我们利用LAMOST DR4的M巨星样本，结合Gaia DR2自行和ALLWISE测光数据，得到了一个非常纯净的人马座（Sgr）流恒星样本。 以TiO5和CaH光谱指数作为指标，从LAMOST DR4光谱中的M矮星中挑选出大量M巨星样本。 综合考虑位置、距离、自行以及角动量分布后，我们得到了164颗纯净的Sgr流恒星。 我们发现，在相同的角动量下，拖尾臂的能量高于前导臂。 我们探测到的拖尾臂在$\sim 130$处延伸至日心距离$\tilde\Lambda_{\odot}\sim 170^{\circ}$千秒差距，这与在RR Lyrae变星中发现的特征一致（\citet{sgr2017}）。 这两种通过M巨星和RR Lyrae变星探测到的人马座Sgr结构均表明，Sgr流可能包含具有广泛金属丰度范围的多个恒星群体。 显示英文摘要

摘要： We use LAMOST DR4 M giants combined with Gaia DR2 proper motions and ALLWISE photometry to obtain an extremely pure sample of Sagittarius (Sgr) stream stars. Using TiO5 and CaH spectral indices as an indicator, we selected out a large sample of M giant stars from M dwarf stars in LAMOST DR4 spectra. Considering the position, distance, proper motion and the angular momentum distribution, we obtained 164 pure Sgr stream stars. We find that the trailing arm has higher energy than the leading arm in same angular momentum. The trailing arm we detected extends to a heliocentric distance of $\sim 130$ kpc at $\tilde\Lambda_{\odot}\sim 170^{\circ}$, which is consistent with the feature found in RR Lyrae in \citet{sgr2017}. Both of these detections of Sgr, in M giants and in RR Lyrae, imply that the Sgr stream may contain multiple stellar populations with a broad metallicity range.