| The jump in X-ray spectral resolution made possible by the orbiting X-ray observatory Chandra has inspired a, host of new techniques for determining the locations, motions, and temperature structures of the X-ray emitting plasma of hot stars. Although steady-state models of stellar winds are relatively well developed, X-rays offer a unique window on small-scale inhomogeneous structures in hot star winds. Currently, the most viable theory of X-ray generation in hot stars relies on small instabilities growing into X-ray emitting shocks distributed throughout the wind. The advent of high-resolution X-ray data allow many new ways to test this paradigm which are applied here.; In a detailed study of the O4f star ζ Pup, X-ray emitting gas is found extremely close to the photosphere, a region where it would be difficult to generate strong shocks. The X-ray line profiles of ζ Pup do conform well to what would be expected from an X-ray source embedded in an expanding, absorbing wind: they are broad due to the wind expansion, and their centroids are blue-shifted due to wind absorption of X-rays originating on the far side of the wind. Achieving an understanding of the line profiles of the O9III star δ Ori is not as straightforward, however. The emission lines are surprisingly narrow and do not show the expected blueshift. Detailed comparisons to theories of line profile generation are not able to resolve this discrepancy.; A study of the six normal hot stars observed with Chandra reveal that the good agreement found between the line profiles of ζ Pup and theoretical expectations is the exception, not the rule. Perhaps most puzzling, the X-ray line profiles of the two B stars studied are only broadened by a couple of hundred km s−1, making it difficult to imagine how the X-ray emitting gas can be related in any way to the rapid outflow of the wind as a whole. A recently proposed infalling clump model for τ Sco can explain nearly all of its X-ray properties. This model probably does not explain all B star X-ray emission, for the other B star studied (β Cru) is a much dimmer and softer X-ray emitter. |
