SIMBAD references

We study the X-ray emission of T Tauri stars (TTS) in Taurus-Auriga as observed with the spatially unbiased flux-limited ROSAT All-Sky Survey. Our detection rates are comparable with Einstein Observatory results: 43 out of 65 (66%) weak-line TTS (WTTS) and 9 out of 79 (11%) classical TTS (CTTS) exhibit X-ray emission above the ROSAT survey detection limit. Spectral fits give results consistent with Raymond-Smith spectra and emission temperatures of ∼1keV for both CTTS and WTTS. However, we find that CTTS and WTTS have significantly different X-ray luminosity functions, even when correcting luminosities for individual X-ray spectra (absorption and emission energy). Medians of X-ray luminosities log (L_X/erg/sec) are 29.701±0.045 for WTTS and 29.091±0.032 for CTTS, all in 140pc distance. A strong correlation between X-ray surface flux and stellar rotation indicates that WTTS are intrinsically more X-ray active than CTTS because WTTS rotate faster. However, rotation is not the only parameter that determines X-ray activity, we find that X-ray luminosity is correlated with stellar mass, bolometric luminosity, effective temperature, and stellar age. Furthermore, X-ray emission of CTTS appears to be harder than that of WTTS.