金牛座分子云中X射线源的光谱学：十颗新的前主序星的发现
Optical spectroscopy of X-ray sources in the Taurus molecular cloud: discovery of ten new pre-main sequence stars
摘要：
我们分析了25个X射线源的光谱，确定为潜在的新成员的金牛座分子云（TMC），以确认其成员在这个SFR。先前在XEST巡天中的X射线源中选择了57个候选者，根据颜色-星等和颜色-颜色图，它们具有与PMS星兼容的2 MASS对应物。我们用TNG望远镜的SARG摄谱仪获得了其中7个候选体的高分辨率光谱，用于寻找Li吸收和测量Ha线以及径向和旋转速度;使用DOLORES获得的其他候选成员的18个低分辨率光谱用于光谱分类，用于Ha测量，并与IR颜色-颜色和颜色-幅度图以及来自X射线数据的附加信息一起评估成员资格。我们发现3个源显示出Li吸收，等效宽度约为500 mA，宽谱线剖面，表明vsin i约为20-40 km/s，径向速度与已知成员一致，以及Ha发射。其中两颗被归类为新的WTTS，而Ha线的EW（~ -9 Ang）及其广泛的不对称轮廓清楚地表明第三颗星（XEST-26-062）是CTTS。用DOLORES观测到的14个源是M型星。15个源显示Ha发射;其中6个具有表明表面重力低于MS星的光谱，并且它们在IR色星等图中的去红位置与它们导出的光谱类型和TMC距离处的PMS模型一致。根据K型星XEST-11-078的Ha发射线强度，确定其为新成员。总体而言，我们确认在光学中观察到的25个X射线源中有10个属于TMC。三个来源仍然不确定。
英文摘要：
We have analyzed optical spectra of 25 X-ray sources identified as potential new members of the Taurus molecular cloud (TMC), in order to confirm their membership in this SFR. Fifty-seven candidates were previously selected among the X-ray sources in the XEST survey, having a 2MASS counterpart compatible with a PMS star based on color-magnitude and color-color diagrams. We obtained high-resolution optical spectra for 7 of these candidates with the SARG spectrograph at the TNG telescope, which were used to search for Li absorption and to measure the Ha line and the radial and rotational velocities; 18 low-resolution optical spectra obtained with DOLORES for other candidate members were used for spectral classification, for Ha measurements, and to assess membership together with IR color-color and color-magnitude diagrams and additional information from the X-ray data. We found that 3 sources show Li absorption, with equivalent widths of ~500 mA, broad spectral line profiles, indicating v sin i ~20-40 km/s, radial velocities consistent with those for known members, and Ha emission. Two of them are classified as new WTTSs, while the EW (~ -9 Ang) of the Ha line and its broad asymmetric profile clearly indicate that the third star (XEST-26-062) is a CTTS. Fourteen sources observed with DOLORES are M-type stars. Fifteen sources show Ha emission; 6 of them have spectra that indicate surface gravity lower than in MS stars, and their de-reddened positions in IR color-magnitude diagrams are consistent with their derived spectral type and with PMS models at the distance of the TMC. The K-type star XEST-11-078 is confirmed as a new member from the strength of its Ha emission line. Overall, we confirm membership to the TMC for 10 out of 25 X-ray sources observed in the optical. Three sources remain uncertain.
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