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X-raying clumped stellar winds | | L.M. Oskinova
; W.-R. Hamann
; A. Feldmeier
; | | Date: |
14 Jun 2008 | | Abstract: | X-ray spectroscopy is a sensitive probe of stellar winds. X-rays originate
from optically thin shock-heated plasma deep inside the wind and propagate
outwards throughout absorbing cool material. Recent analyses of the line ratios
from He-like ions in the X-ray spectra of O-stars highlighted problems with
this general paradigm: the measured line ratios of highest ions are consistent
with the location of the hottest X-ray emitting plasma very close to the base
of the wind, perhaps indicating the presence of a corona, while measurements
from lower ions conform with the wind-embedded shock model. Generally, to
correctly model the emerging X-ray spectra, a detailed knowledge of the cool
wind opacities based on stellar atmosphere models is prerequisite. A nearly
grey stellar wind opacity for the X-rays is deduced from the analyses of
high-resolution X-ray spectra. This indicates that the stellar winds are
strongly clumped. Furthermore, the nearly symmetric shape of X-ray emission
line profiles can be explained if the wind clumps are radially compressed. In
massive binaries the orbital variations of X-ray emission allow to probe the
opacity of the stellar wind; results support the picture of strong wind
clumping. In high-mass X-ray binaries, the stochastic X-ray variability and the
extend of the stellar-wind part photoionized by X-rays provide further strong
evidence that stellar winds consist of dense clumps. | | Source: | arXiv, 0806.2348 | | Services: | Forum | Review | PDF | Favorites | |
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