X-Ray Line Emission from the Hot Stellar Wind of θ1 Orionis C

We present a first emission-line analysis of a high-resolution X-ray spectrum of the stellar wind of θ1 Ori C obtained with the High-Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory. The spectra are resolved into a large number of emission lines from H- and He-like O, Ne, Mg, Si, S, Ar, and Fe ions. The He-like Fe XXV and Li-like Fe XXIV appear quite strong, indicating very hot emitting regions. From H/He flux ratios as well as from Fe He/Li emission measure ratios, we deduce temperatures ranging from 0.5 to 6.1 × 107 K. The He triplets are very sensitive to density as well. At these temperatures the relative strengths of the intercombination and forbidden lines indicate electron densities well above 1012 cm-3. The lines appear significantly broadened, from which we deduce a mean velocity of 770 km s-1 with a spread between 400 and 2000 km s-1. Along with results of the deduced emission measure, we conclude that the X-ray emission could originate in dense and hot regions with a characteristic size of less then 4 × 1010 cm.