The First Direct Measurement of an Early B Supergiant X-ray Source Electron Density

Type Conference Paper
Names Wayne L. Waldron, J. P. Cassinelli, N. A. Miller, E. M. Schlegel
Proceedings Title Bulletin of the American Astronomical Society
Conference Name American Astronomical Society, AAS Meeting #219, #224.02
Date January 1, 2012
Library Catalog NASA ADS
Abstract The ratio of the He-like ion forbidden to intercombination emission lines (f/i) provides a diagnostic for determining either the electron density of an X-ray source (collisional-dominated), or the X-ray source spatial location relative to a central EUV/UV radiation source (radiation-dominated). With the advent of high energy resolution spectroscopy, this diagnostic has become a well proven technique for determining the radial distribution of X-ray sources in OB stellar winds. However, in high energy ions (e.g., Si XIII) where the strength of this ratio is controlled by the radiation shortward of the Lyman edge, we show that there is an expected transition from radiation-dominance to collisional-dominance in the early B star spectral range. Because the photospheric flux is weak in the spectral energy region controlling the Si XIII f/i line ratio, we can probe stellar wind distributed X-ray source models from a different perspective and address fundamental issues pertaining to the origin of OB stellar X-ray emission. To verify this behavior we obtained four Chandra HETGS observations of the early B supergiant κ Ori (B0.5Ia) over a time span of approximately 10 days (total exposure = 234 ks). These observations allow us to explore the expected transition to collisional dominance. But, more importantly, our analysis of the Si XIII f/i line ratio has revealed the first direct measurement of an X-ray source density ( 1013 cm-3). We discuss the implications of these results.
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