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Wind-embedded shocks in FASTWIND: X-ray emission and K-shell absorption

Published online by Cambridge University Press:  28 July 2017

L. P. Carneiro
Affiliation:
LMU Munich, Universitätssternwarte, Scheinerstr. 1, 81679 München, Germany email: luiz@usm.uni-muenchen.de
J. Puls
Affiliation:
LMU Munich, Universitätssternwarte, Scheinerstr. 1, 81679 München, Germany email: luiz@usm.uni-muenchen.de
J. O. Sundqvist
Affiliation:
Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
T. L. Hoffmann
Affiliation:
LMU Munich, Universitätssternwarte, Scheinerstr. 1, 81679 München, Germany email: luiz@usm.uni-muenchen.de
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Abstract

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EUV and X-ray radiation emitted from wind-embedded shocks can affect the ionization balance in the outer atmospheres of massive stars, and can also be the mechanism responsible for producing highly ionized atoms detected in the wind UV spectra. To investigate these processes, we implemented the emission from wind-embedded shocks and related physics into our atmosphere/spectrum synthesis code FASTWIND. We also account for the high energy absorption of the cool wind, by adding important K-shell opacities. Various tests justfying our approach have been described by Carneiro+(2016, A&A 590, A88).

In particular, we studied the impact of X-ray emission on the ionization balance of important elements. In almost all the cases, the lower ionization stages (O iv, N iv, P v) are depleted and the higher stages (N v, O v, O vi) become enhanced. Moreover, also He lines (in particular He ii 1640 and He ii 4686) can be affected as well.

Finally, we carried out an extensive discussion of the high-energy mass absorption coefficient, κν, regarding its spatial variation and dependence on Teff. We found that (i) the approximation of a radially constant κν can be justified for r ⩾ 1.2R* and λ ⩽ 18 Å, and also for many models at longer wavelengths. (ii) In order to estimate the actual value of this quantity, however, the He ii background needs to be considered from detailed modeling.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2017