IDENTIFICATION OF A COMPLETE SAMPLE OF NORTHERN ROSAT ALL-SKY SURVEY X-RAY SOURCES - VI - K-TYPE TO M-TYPE STARS SOUTH OF TAURUS-AURIGA

We present first results of a spectroscopic study of lithium absorptio n 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 optic ally identified by our group. No selection criteria other than requiri ng RASS count rates larger than 0.03 cts s(-1) were applied. The stars are located at galactic latitudes \b(11)\ between 28 degrees and 45 d egrees in an area similar to 20 degrees south of the Taurus-Auriga sta r forming region. In the sample of 35 stars with spectral types betwee n K0 and M5 we found 9 stars with significant LiI lambda 6708 absorpti on lines, 8 K stars and 1 M0 star. No lithium was found in stars with spectral types later than M0. The Li I equivalent widths (corrected fo r the contribution of Fe I) are between similar to 150 m Angstrom and similar to 400 m Angstrom. The lithium strength of these stars is cons istent with ages on the order of 10-30 Myr. These stars are still in a pre-main sequence evolutionary stage, and belong to the weak-line Tau ri stars.