Star formation at high galactic latitude

The star-formation capability of three low-extinction translucent molecular clouds at high galactic latitude is investigated. In addition, a comparison is made between the translucent molecular clouds investigated in this study and the few (star-forming and non-star-forming) dark clouds also found at high galactic latitude. Possible pre-main sequence stars in and around three well studied translucent molecular clouds (MBM7, 40, & 55) have been identified by inspecting ROSAT All-Sky Survey observations in large areas around the clouds and ROSAT pointed observations of the cores of the three clouds. In addition, ROSAT pointed observations of the cores in four other translucent molecular clouds and three dark clouds at high galactic latitude are discussed in the appendix. Follow-up optical spectroscopy of stellar candidates with {dollar}msb{lcub}v{rcub} sbsp{lcub}sim{rcub}{lcub}<{rcub} 15.5{dollar} mag was conducted with the 1.5-m Fred Lawrence Whipple Observatory telescope to identify standard signatures of pre-main sequence stars (i.e., lithium {dollar}lambda{dollar}6708 A absorption and H{dollar}alpha{dollar} emission). We found 16 X-ray bright, lithium-rich stars near several of the molecular clouds. Relative ages for these stars are estimated by their position on a W(Li) v. T{dollar}sb{lcub}rm eff{rcub}{dollar} diagram, using a calibration derived from data for several clusters with known ages. Most of the stars have a measured W(Li) that is consistent with their being roughly the age of the Pleiades ({dollar}sim{dollar}10{dollar}sp8{dollar} yr) or the Hyades ({dollar}sim{dollar}8 {dollar}times{dollar} 10{dollar}sp8{dollar} yr)--although a few may be slightly younger than the Pleiades. However, these stars are almost surely not T Tauri stars. Instead, they are probably part of the population of X-ray active, lithium-rich stars recently identified by ROSAT and Einstein observations in low gas-density regions. Since the translucent high-latitude clouds are believed to be relatively young objects ({dollar}sim{dollar}10{dollar}sp6{dollar} yr), it is unlikely that the 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, low column density clouds, such as the translucent clouds discussed in this dissertation, can support star-formation.