半透明云MBM 18（LDN 1569）中的分子气体和恒星
Molecular gas and stars in the translucent cloud MBM 18 (LDN 1569)
摘要：
在对MBM 18的1平方度区域进行的客观棱镜巡天中发现的10颗候选H-α发射线恒星中，有7颗被光谱观测到。其中4个有弱的H-α发射，7个中有6个有M1-M4 V光谱类型。其中一颗恒星的类型为F7-G1 V，吸收的是H-α。其中三颗M星的光谱可能显示出LiI的吸收线，尽管这些都不是明确的探测。对于六个M-星的一个很好的拟合获得与前主序等时线表明年龄在7.5和1500万年之间。由12 CO（1-0）辐射积分得到的分子云质量为160 Mo（距离为120 pc），比维里质量（10^3 Mo）小得多，并且云没有引力束缚。也不是我们通过一个团块发现程序确定的单个团块。考虑到相对较弱或没有H-α发射，没有其他发射线，也没有明显的LiI吸收，目标不是金牛T星。它们的年龄在750万年到1500万年之间，足以解释它们光谱中缺乏锂的原因。根据推导出的距离（60- 250 pc），有些恒星可能位于分子云（120- 150 pc）内。从云作为一个整体，以及单独的团块，不受引力约束的事实，结合恒星的年龄，我们得出结论，（这些）恒星不太可能在MBM 18中形成。
英文摘要：
Seven of ten candidate H-alpha emission-line stars found in an objective grism survey of a 1 square degree region in MBM 18, were observed spectroscopically. Four of these have weak H-alpha emission, and 6 out of 7 have spectral types M1-M4V. One star is of type F7-G1V, and has H-alpha in absorption. The spectra of three of the M-stars may show an absorption line of LiI, although none of these is an unambiguous detection. For the six M-stars a good fit is obtained with pre-main-sequence isochrones indicating ages between 7.5 and 15Myr. The molecular cloud mass, derived from the integrated 12CO(1-0) emission, is 160Mo (for a distance of 120pc), much smaller than the virial mass (10^3Mo), and the cloud is not gravitationally bound. Nor are the individual clumps we identified through a clump-finding routine. Considering the relative weakness or absence of the H-alpha emission, the absence of other emission lines, and the lack of clear LiI absorption, the targets are not T Tauri stars. With ages between 7.5 and 15Myr they are old enough to explain the lack of lithium in their spectra. Based on the derived distances (60-250pc), some of the stars may lie inside the molecular cloud (120-150pc). From the fact that the cloud as a whole, as well as the individual clumps, are not gravitationally bound, in combination with the ages of the stars we conclude that it is not likely that (these) stars were formed in MBM 18.
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