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A key factor in the analysis of X-ray data from OB stars is determining the true nature of the X-ray absorption, i.e., the relative strengths of the "local" and ISM absorption components. The local component is in addition to the fixed ISM absorption and refers to the X-ray attenuation caused by the massive, highly ionized stellar wind. Determining the strength of this local component is crucial to understanding the X-ray production mechanism in these stars. Although observational evidence supporting the existence of wind absorption has increased somewhat over the past few years, a clear physical picture of the significance of this component has not emerged. In this study, we discuss the characteristic X-ray signatures of wind absorption. We demonstrate how PSPC and IPC hardness ratio data can be used as an effective diagnostic tool for establishing the presence of stellar wind absorption. To show the importance of this local component, we present detailed spectral analyses of PSPC data for several OB stars. Used in conjunction with IPC data, we find that stringent constraints can be placed on the strength of the local absorption component. From the strength of this component, the X-ray source location, relative to the stellar reference frame, can be ascertained. The implications of our results, with respect to the various proposed X-ray production models, are discussed.
This work was supported in part by NASA contract NAS5-31220.
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