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N.A. Miller, J.P. Cassinelli (Univ. of Wisconsin-Madison), J.J. MacFarlane (Prism Computational Sciences)
We have observed \delta Ori (O9.5II) using the High Energy Transmission Grating (HETG) on board Chandra. \delta Ori is among the best-studied early-type X-ray sources, with measurements from a number of satellites including ROSAT and ASCA. Our high-resolution (\delta v \approx 500 km/s) MEG spectrum shows resolved emission lines of ions ranging from helium-like silicon, to hydrogen- and helium-like magnesium, neon, and oxygen. Most of the iron lines which are present are attributable to Fe XVII. The broadening of the emission lines indicates that the X-rays are formed out in the wind, but with a broadening less than the terminal velocity of 2290 km/s. We begin with a simple isothermal expanding shell model to explain the broadening of the lines, and then apply successively more complex models. New atomic calculations by Wang Ping of Forbidden, Intercombination, and Resonance (FIR) line complexes for helium-like ions are used to constrain the density in the X-ray emitting regions. The derived densities are then compared with the range of ambient wind densities. We would like to thank NASA for support of this project under grant NAG5-9226.