NEW WEAK-LINE T-TAURI STARS IN TAURUS-AURIGA

On the basis of the ROSAT All-Sky-Survey, a study of the Taurus-Auriga star forming region has been performed in order to search for hithert o undiscovered T Tauri stars. Our study covers an area of about 280 sq uare degrees, located between 4(h) and 5(h) in right ascension and bet ween 15 degrees and 34 degrees in declination. Identification of ROSAT All-Sky Survey sources in this area by means of optical spectroscopy revealed 2 new classical T Tauri stars (CTTS) and 66 new weak-line-T T auri stars (WTTS) with W-lambda(H alpha) less than or equal to 10 Angs trom. Additional pointed ROSAT observations led to the identification of 6 more WTTS and 2 CTTS, giving a total of 76 new T Tauri stars. The large area of our study, as compared with previous works, allows us t o study the spatial distribution of WTTS in this star forming region. We find the WTTS of our survey to be distributed over the whole region investigated. There is a noticeable decline of the surface density fr om south to north within our study area, but the spatial distribution extends most probably beyond our study region. No clustering towards t he population of T Tauri stars known prior to ROSAT in Taurus-Auriga c ould be observed. We suggest that the WTTS found in our study might in part be somewhat older than the previously known T Tauri stars in Tau rus-Auriga, and that their broad spatial distribution is due to the ty pical velocity dispersion of a few km/s measured for Taurus T Tauri st ars, in which case for some of our WTTS an age on the order of 10(7) y ears would be required for reaching the observed distances from the Ta urus dark clouds. We estimate a WTTS/CTTS ratio of about 6 within our study area, but conclude that because of the different spatial distrib ution of WTTS and CTTS this ratio will be most probably significantly larger for a more extended area.