1998A&A...339..457Z

We present first results of a spectroscopic study of lithium absorption lines in late-type stars at high galactic latitude. The investigated stars were identified previously as optical counterparts of ROSAT All-Sky Survey sources. They are contained in a complete X-ray count-rate limited representive subsample of the RASS which was completely optically identified by our group. No selection criteria other than requiring RASS count rates larger than 0.03cts/s were applied. The stars are located at galactic latitudes |b^II| between 28° and 45° in an area ∼20° south of the Taurus-Auriga star forming region. In the sample of 35 stars with spectral types between K0 and M5 we found 9 stars with significant LiIλ6708 absorption lines, 8K stars and 1M0 star. No lithium was found in stars with spectral types later than M0. The LiI equivalent widths (corrected for the contribution of FeI) are between ∼150mÅ and ∼400mÅ. The lithium strength of these stars is consistent with ages on the order of 10-30Myr. These stars are still in a pre-main sequence evolutionary stage, and belong to the weak-line Tauri stars.