ABSTRACT. We present first results of a high-resolution X-ray observation of the nearby Wolf-Rayet binary system γ² Velorum (WC8 + O7.5) using the Chandra High-Energy Transmission Grating (HETG). Emission lines from Mg, Si, S, Ne, and Fe dominate the spectrum and imply a range of plasma temperatures from ~4 MK up to at least ~25 MK. The strongest lines are broadened, but no Doppler shifts are detected. He-like triplets show strong forbidden lines with no significant weakening from collisional effects or photoexcitation, contrasting sharply with the diluted forbidden lines of single O-type supergiants such as ζ Puppis. These results imply that some lines such as the Ne IX triplet are formed in cooler plasma at tens of stellar radii or more from the O star, well outside of the central wind interaction region located near the O star surface. Lastly, we report the discovery of a new X-ray source lying only 48 north of γ² Vel that is very likely a low-mass pre-main-sequence star.

Subject headings: stars: individual (γ2 Velorum, HD 68273); stars: Wolf-Rayet; X-rays: stars

Print publication: Issue 2 (2001 September 10)
Received 2001 May 16, accepted for publication 2001 July 30
Published 2001 August 23