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S. Skinner (Univ. of Colorado - Boulder), S. Zhekov (Space Research Institute - Sofia, Bulgaria), M. Audard (Columbia Univ.), M. Gagne (West Chester Univ.), M. Guedel (Paul Scherrer Inst. - Villigen, Switz.)
We present an overview of recent Chandra and XMM-Newton observations of massive young stars whose goal is to clarify the origin of their X-ray emission. Theoretical models predict soft X-rays at kT < 1 keV from radiative wind shocks but the detection of hotter plasma in some massive young OB stars suggests that magnetic processes may be important at early evolutionary stages. Chandra grating spectra of the young binary system HD 150136 (O5V + O6; SB2; Porb = 2.7 d) in the core of the open cluster NGC 6193 show heavily broadened emission lines with no significant asymmetry and an emission measure distribution dominated by cool plasma at kT < 1 keV, suggesting a wind shock origin. We examine the possibility that intrinsic X-ray emission arising in the O-star winds is augmented by a cool colliding wind shock component from the wind-wind interaction region at close binary separations of a few stellar radii where radiative cooling is expected to be important. At earlier evolutionary stages, we report the Chandra detection of X-ray emission from the luminous infrared source IRS 2b in NGC 2024 (Orion B), which is thought to be a young embedded OB star. Finally, we present XMM-Newton CCD X-ray spectra of the Herbig star HD 104237 (A4e), a rare nearby intermediate mass (~2 solar masses) pre-main-sequence star. The spectra show emission lines and hot plasma at kT ~ 3 keV. Such high temperatures are not expected from wind or accretion shocks in an A-type star, implying a magnetic origin. A putative low-mass companion such as a T Tauri star could be contributing to the X-ray emission but the close agreement between the X-ray and optical positions obtained from higher resolution Chandra observations leaves open the possibility that some of the X-ray emission is intrinsic to the Herbig star itself. This research has been funded by NASA grants NAG5-10326 (GSFC), GO1-2009A (SAO), and GO2-3025 X (SAO).
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.