X-Ray-Induced Ionization in the Winds of Early-B Stars: Constraints Imposed by EUVE

Hot stars are losing mass at large rates through their high-speed winds. Such stars are also know to emit X-rays with L_X/L_bol =~ 10(-7) for O stars, falling to =~ 10(-9) for B3 stars. It is particularly difficult to observationally determine the wind properties of early-B stars because their UV wind lines are typically very weak. In this study we use He II emission lines detected by EUVE to determine the wind properties of epsilon CMa. We find that the He II emission lines most likely originate from He III recombination in the ``cool'' portion of the wind, and is a byproduct of X-ray photoionization of He. The conditions of the X-ray emitting region are determined by the strengths of Fe IX - Fe XVI lines observed by EUVE. It has also been found that the He II Lyalpha line likely produces the observed O III line emission at 374 Angstroms via the Bowen mechanism.