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Long known to be an unusual early-type star by virtue of its hard and strongX-ray emission, tau Scorpii poses a severe challenge to the standard picture ofO-star wind-shock X-ray emission. The Chandra HETGS spectrum now providessignificant direct evidence that this B0.2 star does not fit this standardwind-shock framework. The many emission lines detected with the Chandragratings are significantly narrower than what would be expected from a starwith the known wind properties of tau Sco, although they are broader than thecorresponding lines seen in late-type coronal sources. While line ratios areconsistent with the hot plasma on this star being within a few stellar radii ofthe photosphere, from at least one He-like complex there is evidence that theX-ray-emitting plasma is located more than a stellar radius above thephotosphere. The Chandra spectrum of tau Sco is harder and more variable thanthose of other hot stars, with the exception of the young magnetized O startheta Ori C. We discuss these new results in the context of wind, coronal, andhybrid wind-magnetic models of hot-star X-ray emission.

High‐ResolutionChandraSpectroscopy of τ Scorpii: A Narrow‐Line X‐Ray Spectrum from a Hot Star