1999A&A...341..163H

The star formation capability of two molecular clouds at high galactic latitude (|b|>30°) is investigated. Possible pre-main sequence stars in and around the translucent clouds MBM7 and MBM55 have been identified via their X-ray emission by inspecting ROSAT All-Sky Survey observations of the clouds and environs and ROSAT pointed observations of the high-density cores within the clouds. Follow-up optical spectroscopy of the stellar X-ray sources with V≤15.5mag was conducted with the 1.5-m Fred Lawrence Whipple Observatory telescope to identify standard signatures of pre-main sequence stars (LiI λ6708Å absorption and Hα emission). We found 11 stars which have lithium equivalent widths, W(Li), above our detection threshold. Three of the stars with lithium also have weak Hα emission. Relative ages for the stars with lithium are estimated by their position on an W(Li) vs. T_eff diagram. A calibration derived from data for several clusters with known ages indicates the stars are older than the translucent high-latitude clouds. This conclusion is supported by a comparison with theoretical evolutionary tracks of the stars from our sample for which we have distance measurements from Hipparcos. We find it is unlikely that any of the X-ray active, lithium-rich stars we identified have formed in the clouds in question. Theoretical and observational arguments support this conclusion and render unlikely the possibility that low-extinction translucent clouds are the sites of star formation.