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A search for star formation in the translucent clouds MBM7 and MBM55
The star formation capability of two molecular clouds at high galacticlatitude ( | b | > 30(deg) ) is investigated. Possible pre-mainsequence stars in and around the translucent clouds MBM7 and MBM55 havebeen identified via their X-ray emission by inspecting ROSAT All-SkySurvey observations of the clouds and environs and ROSAT pointedobservations of the high-density cores within the clouds. Follow-upoptical spectroscopy of the stellar X-ray sources with V <= 15.5 magwas conducted with the 1.5-m Fred Lawrence Whipple Observatory telescopeto identify standard signatures of pre-main sequence stars (LiI<~mbda6708 Angstroms absorption and Hα emission). We found 11stars which have lithium equivalent widths, W(Li), above our detectionthreshold. Three of the stars with lithium also have weak Hαemission. Relative ages for the stars with lithium are estimated bytheir position on an W(Li) vs. T_eff diagram. A calibration derived fromdata for several clusters with known ages indicates the stars are olderthan the translucent high-latitude clouds. This conclusion is supportedby a comparison with theoretical evolutionary tracks of the stars fromour sample for which we have distance measurements from Hipparcos. Wefind it is unlikely that any of the X-ray active, lithium-rich stars weidentified have formed in the clouds in question. Theoretical andobservational arguments support this conclusion and render unlikely thepossibility that low-extinction translucent clouds are the sites of starformation. Table~3 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html.
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