EINSTEIN OBSERVATIONS OF T-TAURI STARS IN TAURUS-AURIGA .1. PROPERTIES OF X-RAY-EMISSION

We present a systematic reanalysis of the Einstein IPC X-ray data on the pre-main-sequence stars in the Taurus-Auriga star formation region. We consider all cataloged stars in this region which have been observed with the IPC; of these, 52 out of 68 can be identified with X-ray sources; upper limits on the X-ray luminosity have been evaluated in the remaining cases. We derive an X-ray luminosity function and argue that its median L(x) is representative of the population intrinsic value, in spite of incompleteness of the sample and possible ambiguities in the X-ray source identifications. As a result, it is confirmed that the known steady increase in the average level of X-ray emission toward younger ages can be extended to the pre-main-sequence phase. By using the line equivalent width as the relevant parameter, a statistically significant difference is found between the distributions of X-ray luminosities of stars with and without strong emission lines. No such difference is found instead between stars with and without strong infrared excess at 25 mu m.