1999AJ....118.1354B

We present the results of a moderately deep, wide-field optical/X-ray survey extending over ∼60° 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 previous surveys. We identify four new T Tauri stars, two in the area of L1500 and L1503, one in L1538, and one in L1544. X-rays were detected from three near-IR sources, one of them a very reddened Class II T Tauri star. Four X-ray sources have no known optical/IR known counterpart; they could be very reddened pre-main-sequence stars. Our findings are consistent with the idea that little (if any) star formation has taken place in L1537 and L1538. Although we found one slightly older T Tauri star (∼3-4 Myr old), our survey yields no evidence for any significant number of T Tauri stars, regardless of mass and age, outside the main groups of young stars in Taurus. We conclude that the M stars comprising the low-mass end of the ROSAT All-Sky Survey (RASS) source population must be older than ∼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 vicinity.