ASCA SOLID-STATE IMAGING SPECTROMETER OBSERVATIONS OF O-STARS

We report ASCA Solid State Imaging Spectrometer (SIS) X-ray observatio ns of the O stars delta Ori and lambda Ori. The energy resolution of t he SIS allows us to resolve features in the O star X-ray spectra which are not apparent in spectra obtained by X-ray spectrometers with lowe r energy resolution. SIS spectra from both stars show evidence of line emission, suggesting the thermal nature of the X-ray source. However, the observed line strengths are different for the two stars. The obse rved stellar X-ray spectra are not well described by isothermal models although absorbed thermal emission models with two or more temperatur es can provide an adequate fit to the data. For both stars we present evidence of absorbing columns significantly larger than the known ISM columns, indicative of absorption by a circumstellar medium, presumabl y the stellar winds. In addition, the lambda Ori spectrum shows the pr esence of emission at energies >3 keV which is not seen in the delta O ri spectrum.