X-Ray-Induced Ionization in the Winds of Early-B Stars: Constraints Imposed by EUVE
Session 80 -- Stellar Activity II: Early Type Stars, Normal Stars
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

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

J.J.MacFarlane, D.H.Cohen, J.P.Cassinelli (Univ. of Wisconsin)

Hot stars are losing mass at large rates through their high-speed winds. Such stars are also know to emit X-rays with $L_{X}/L_{bol}$ $\simeq$ $10^{-7}$ for O stars, falling to $\simeq$ $10^{-9}$ 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 Ly$\alpha$ line likely produces the observed O~III line emission at 374~\AA~via the Bowen mechanism.