X-ray emission from young stars in the Tucanae association

We report on X-ray emission from members of the recently discovered Tucanae association, a group of stars with youth signatures and similar space motion. The Tucanae association is the nearest known region of recent star formation (similar to 45 pc) far from molecular clouds (Zuckerman & Webb 2000). We have made use of the ROSAT Data Archive and searched for X-rays from Tucanae stars in both ROSAT All-Sky Survey (RASS) and pointed observations. While the RASS provides complete coverage of the sky, only three potential Tucanae members have been observed during PSPC pointings. Ail three stars have been detected. For the RASS the percentage of detections is 59%. The comparison of the X-ray luminosity function of Tucanae to that of other star forming regions may provide clues to the uncertain age of the association. We find that the distribution of X-ray luminosities is very similar to the ones derived for the TW Hya association, the Taurus-Auriga T Tauri Stars, and the IC 2602 cluster, but significantly brighter than the luminosity distribution of the Pleiades. We conclude that the stars in Tucanae are most likely young, on the order of 10 - 30 Myr. Strong variability of most stars emerges from the X-ray lightcurves where several flares and irregular variations are observed.