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

Motivated by recent detections by the XMM and Chandra satellites of X-rayline emission from hot, luminous stars, we present synthetic line profiles forX-rays emitted within parameterized models of a hot-star wind. The X-ray lineemission is taken to occur at a sharply defined co-moving-frame resonancewavelength, which is Doppler-shifted by a stellar wind outflow parameterized bya `beta' velocity law, $v(r)=v_{\infty} (1-\R_{\ast}/r)^\beta$. Above someinitial onset radius $R_o$ for X-ray emission, the radial variation of theemission filling factor is assumed to decline as a power-law in radius, $f(r)\sim r^{-q}$. The computed emission profiles also account for continuumabsorption within the wind, with the overall strength characterized by acumulative optical depth $\tau_\ast$. In terms of a wavelength shift fromline-center scaled in units of the wind terminal speed $v_{\infty}$, we presentnormalized X-ray line profiles for various combinations of the parameters$\beta$, $\tau_\ast$, $q$ and $R_o$, and including also the effect ofinstrumental broadening as characterized by a Gaussian with a parameterizedwidth $\sigma$. We discuss the implications for interpreting observed hot-starX-ray spectra, with emphasis on signatures for discriminating between``coronal'' and ``wind-shock'' scenarios. In particular, we note that inprofiles observed so far the substantial amount of emission longward of linecenter will be difficult to reconcile with the expected attenuation by the windand stellar core in either a wind-shock or coronal model.