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Seven of ten candidate H-alpha emission-line stars found in an objectivegrism survey of a 1 square degree region in MBM 18, were observedspectroscopically. Four of these have weak H-alpha emission, and 6 out of 7have spectral types M1-M4V. One star is of type F7-G1V, and has H-alpha inabsorption. The spectra of three of the M-stars may show an absorption line ofLiI, although none of these is an unambiguous detection. For the six M-stars agood fit is obtained with pre-main-sequence isochrones indicating ages between7.5 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 individualclumps we identified through a clump-finding routine. Considering the relativeweakness or absence of the H-alpha emission, the absence of other emissionlines, 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 oflithium in their spectra. Based on the derived distances (60-250pc), some ofthe stars may lie inside the molecular cloud (120-150pc). From the fact thatthe cloud as a whole, as well as the individual clumps, are not gravitationallybound, in combination with the ages of the stars we conclude that it is notlikely that (these) stars were formed in MBM 18.

Molecular gas and stars in the translucent cloud MBM 18 (LDN 1569)