X-RAY EMISSION FROM EARLY-TYPE STARS: NEW RESULTS AND NEW CHALLENGES

摘要

Early-type stars of spectral types O and Wolf-Rayet are moderately bright X-ray sources. The X-ray emission is usually attributed to a shock-heated plasma. In single stars the shocks could arise from the intrinsic instability of the stellar winds, whilst in binary systems, the collision of the two stellar winds can provide an additional emission. XMM-Newton and Chandra have observed a number of these stars, obtaining spectra of unprecedented quality. These observations provide new insight into the properties of the hot plasma in early-type stars winds, but raise also new questions that challenge our 'standard' model for the X-ray emission of hot stars. In this review, I highlight some of the most important results obtained over the last six years.