Stassun, X-ray properties of young stars and stellar clusters

Although the environments of star and planet formation are thermodynamically cold, substantial X-ray emission from 10 − 100 MK plasmas is present. In low mass pre-main sequence stars, X-rays are produced by violent magnetic reconnection flares. In high mass O stars, they are produced by wind shocks on both stellar and parsec scales. The recent Chandra Orion Ultradeep Project, XMM-Newton Extended Survey of Taurus, and Chandra studies of more distant high-mass star forming regions reveal a wealth of X-ray phenomenology and astrophysics. X-ray flares mostly resemble solar-like magnetic activity from multipolar surface fields, although extreme flares may arise in field lines extending to the protoplanetary disk. Accretion plays a secondary role. Fluorescent iron line emission and absorption in inclined disks demonstrate that X-rays can efficiently illuminate disk material. The consequent ionization of disk gas and irradiation of disk solids addresses a variety of important astrophysical issues of disk dynamics, planet formation, and meteoritics. New observations of massive star forming environments such as M 17, the Carina Nebula and 30 Doradus show remarkably complex X-ray morphologies including the low-mass stellar population, diffuse X-ray flows from blister HII regions, and inhomogeneous superbubbles. X-ray astronomy is thus providing qualitatively new insights into star and planet formation. 1