X-Ray Emission from O-Stars

Abstract

The X-ray emission mechanism of OB stars is still an unresolved problem. One possible emission mechanism involves hot gases produced by periodic shocks ploughing through the wind (Lucy & White 1980; Lucy 1982). Coronal models are viable alternatives: A photoionized hot corona can explain the observed soft X-ray spectra of OB stars. In this case, however, the origin of the hot corona is a problem (Stewart & Fabian 1981; Waldron 1984). A crucial key point to distinguish the above two models might be high quality measurements of soft X-ray spectra in order to confirm emission lines and absorption edges. So far, some detections of line emission have been reported (Cassinelli & Swank 1983; Corcoran et al. 1994; Kitamoto & Mukai 1996). These emission lines definitely indicate that the X-ray emission is thermal. But still the origin of the high temperature plasma is an open problem. In this work, we report ASCA SIS (Tanaka, Inoue & Holt 1994) observation results of four 0 stars: ζ Ori, λ Ori, δ Ori and ζ Pup.