[ITAL]Chandra[/ITAL] Detection of a Close X-Ray Companion and Rich Emission-Line Spectrum in the Wolf-Rayet Binary γ Velorum

We present first results of a high-resolution X-ray observation of the nearby Wolf-Rayet binary system γ 2 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 4 8 north of γ 2 Vel that is very likely a low-mass pre-main-sequence star.