Combining EUVE with ROSAT Observations to Locate the X-ray Emission in the Winds of Early B-Stars

We fit empirical wind-shock emission models to ROSAT PSPC and short-wavelength EUVE observations of five stars with spectral types B1 or B2. The models assume optically thin thermal plasma emission (continuum plus lines) with a distribution of source temperatures. We also include absorption by wind material of varying ionization balance. These models are designed to approximate the output of hydrodynamical simulations of radiation-driven winds, which predict that shocks will be present in the wind beyond a few tenths of a stellar radius. Many early B stars have been discovered by ROSAT to be soft X-ray emitters. These data have, however, not been able to constrain the degree of X-ray absorption in the wind, or even to confirm the presence of wind absorption of X-rays. By including the EUVE observations in the analysis, we are able to rule out models which do not contain significant amounts of wind absorption (especially by helium). These results imply that much of the B star wind emission between 504 Angstroms and about 100 Angstroms does not escape the wind.