Session 7 - Molecular Clouds.
Display session, Wednesday, January 07
Exhibit Hall,

## [7.17] An X-ray Survey of Very Young Stellar Objects

L. Carkner, J. A. Kozak, E. D. Feigelson (Penn State)

T Tauri stars have long been known to be strong and variable X-ray emitters, but only recently has such emission been detected from the younger protostellar stage. A search for X-ray emission from such very young stars is conducted using data from the ROSAT archive of pointed observations. Our initial sample is drawn from three lists of objects with protostellar properties: Herbig-Haro outflow sources from Reipurth (1993), low temperature objects in near-by star forming regions from Chen et al. (1995), and CO outflow sources from Fukui et al. (1993). About 150 of these lie in ROSAT fields. None are detected at the 3 sigma limit over the 1-2.4 keV band. The sources have upper limits of 1-9 counts per kilosecond, which at the distances of 130-2200 pc corresponds to log L = 29-32 ergs s^-1, assuming a plasma temperature of 2.2 keV and N_H = 10^22. We also report on ASCA pointed observations of the Barnard 5 and Lynds 723 clouds. The 5 protostars in these fields are not detected down to levels of \sim2 \times 10^30 ergs s^-1 over the energy range 0.5-10 keV. We conclude that X-ray emission from protostars is either uncommon or the result of infrequent flaring.