X‐Ray Line Profiles from Parameterized Emission within an Accelerating Stellar Wind

Abstract

Motivated by recent detections by the XMM and Chandra satellites of X-ray line emission from hot, luminous stars, we present synthetic line proÐles for X-rays emitted within parameterized models of a hot-star wind. The X-ray line emission is taken to occur at a sharply deÐned comoving-frame resonance wavelength, which is Doppler-shifted by a stellar wind outÑow parameterized by a "" b ÏÏ velocity law, Above some initial onset radius for X-ray emission, the radial variation of the v(r) \ v = (1 [ R * /r)b. R o emission Ðlling factor is assumed to decline as a power law in radius, f (r) D r~q. The computed emission proÐles also account for continuum absorption within the wind, with the overall strength characterized by a cumulative optical depth In terms of a wavelength shift from line center scaled in units of the q *. wind terminal speed we present normalized X-ray line proÐles for various combinations of the pa-v = , rameters b, q, and and also including the e †ect of instrumental and/or macroturbulent broadening q * , R o as characterized by a Gaussian with a parameterized width p. We discuss the implications for interpreting observed hot-star X-ray spectra, with emphasis on signatures for discriminating between "" coronal ÏÏ and "" wind-shock ÏÏ scenarios. In particular, we note that in proÐles observed so far the substantial amount of emission longward of line center will be difficult to reconcile with the expected attenuation by the wind and stellar core in either a wind-shock or coronal model.