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| Paper: |
The X-Ray View of OB Star Wind Structure and Dynamics |
| Volume: |
464, Circumstellar Dynamics at High Resolution |
| Page: |
267 |
| Authors: |
Cohen, D. H. |
| Abstract: |
High-resolution X-ray grating spectroscopy enables us to measure the
kinematics and spatial distribution of the shock-heated wind plasma
in O and early B stars, testing the predictions of the embedded wind
shock scenario of massive star X-ray production. By fitting models
to the resolved, Doppler broadened X-ray emission line profiles
measured by the Chandra X-ray Observatory's grating
spectrometer, we find an onset radius of X-ray production of roughly
Ro = 1.5 R★ for the O supergiants, ζ Pup
and HD 93129A. From the profile fitting we also find that the
terminal velocity of the X-ray emitting plasma is consistent with
that of the bulk, UV absorbing wind. We also use the X-ray emission
line profiles to measure the wind mass-loss rates and break the
degeneracy between mass-loss rate and clumping factor that affects
traditional Hα and radio free-free diagnostics. We find
clumping factors of order fcl = 10, which also agrees with
the simulations of the wind instability. And we find that clumping
begins very close to the photosphere, significantly lower in the
wind than the onset of X-ray production. For lower density B star
winds, the X-ray emission lines are much narrower than in the O
supergiants, and are inconsistent with the hot plasma sharing the
kinematics of the bulk wind. |
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