SIMBAD references

The Chandra spectrum of δ Ori A shows emission lines from hydrogen- and helium-like states of Si, Mg, Ne, and O, along with N VII Lyα and lines from ions in the range Fe XVII-Fe XXI. In contrast to the broad lines seen in ζ Pup and ζ Ori (850±40 and 1000±240 km.s^–1 half-width at half-maximum [HWHM], respectively), these lines are broadened to only 430±60 km.s^–1 HWHM. This is much lower than the measured wind terminal velocity of 2000 km.s^–1. The forbidden, intercombination, and resonance (fir) lines from He-like ions indicate that the majority of the X-ray line emission does not originate at the base of the wind, in agreement with the standard wind shock models for these objects. However, in that model the X-ray emission is distributed throughout an expanding, X-ray-absorbing wind, and it is therefore surprising that the emission lines appear relatively narrow, unshifted, and symmetric. We compare the observed line profiles to recent detailed models for X-ray line profile generation in hot stars, but none of them offers a fully satisfactory explanation for the observed line profiles.