A large-scale objective-prism and X-ray survey in Taurus-Auriga

We present the results of a moderately deep, wide-held optical/X-ray survey extending over similar to 60 degrees in the Taurus-Auriga molecular cloud complex. Our observations are sensitive enough to allow us to detect lower mass and older pre-main-sequence stars that could have been missed in previ ous surveys. We identify four new T Tauri stars, two in the area of L1500 a nd L1503, one in L1538, and one in L1544. X-rays were detected from three n ear-IR sources, one of them a very reddened Class II T Tauri star. Four X-r ay sources have no known optical/R known counterpart; they could be very re ddened premain-sequence stars. Our findings are consistent with the idea th at little (if any) star formation has taken place in L1537 and L1538. Altho ugh we found one slightly older T Tauri star (similar to 3-4 Myr old), our survey yields no evidence for any significant number of T Tauri stars, rega rdless of mass and age, outside the main groups of young stars in Taurus. W e conclude that the M stars comprising the low-mass end of the ROSAT All-Sk y Survey (RASS) source population must be older than similar to 10 Myr and most probably unrelated to the ongoing process of star formation in Taurus. Instead, the bulk of the RASS sources seen toward regions like Taurus seem to trace the history of star formation over a longer period in the solar v icinity.