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À propos de : Atmospheric NLTE models for the spectroscopic analysis of blue stars with winds        

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  • V. Complete comoving frame transfer, and updated modeling of X-ray emission
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  • Atmospheric NLTE models for the spectroscopic analysis of blue stars with winds
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Abstract
  • Context. Obtaining precise stellar and wind properties and abundance patterns of massive stars is crucial to understanding their nature and interactions with their environments, as well as to constrain their evolutionary paths and end-products. Aims. To enable higher versatility and precision of the complete ultraviolet (UV) to optical range, we improve our high-performance, unified, NLTE atmosphere and spectrum synthesis code  FASTWIND. Moreover, we aim to obtain an advanced description of X-ray emission from wind-embedded shocks, consistent with alternative modeling approaches. Methods. We include a detailed comoving frame radiative transfer for the essential frequency range, but still apply methods that enable low turnaround times. We compare the results of our updated computations with those from the alternative code  CMFGEN, and our previous  FASTWIND version, for a representative model grid. Results. In most cases, our new results agree excellently with those from  CMFGEN, both regarding the total radiative acceleration, strategic optical lines, and the UV-range. Moderate differences concern He  IIλλ4200-4541 and N  Vλλ4603-4619. The agreement regarding N  IIIλλ4634−4640−4642 has improved, though there are still certain discrepancies, mostly related to line overlap effects in the extreme ultraviolet, depending on abundances and micro-turbulence. In the UV range of our coolest models, we find differences in the predicted depression of the pseudo-continuum, which is most pronounced around Ly α. This depression is larger in  CMFGEN, and related to different Fe  IV atomic data. The comparison between our new and previous  FASTWIND version reveals an almost perfect agreement, except again for N  Vλλ4603-4619. Using an improved, depth-dependent description for the filling factors of hot, X-ray emitting material, we confirm previous analytic scaling relations with our numerical models. Conclusions. We warn against uncritically relying on transitions, which are strongly affected by direct or indirect line-overlap effects. The predicted UV-continuum depression for the coolest grid-models needs to be checked, both observationally, and regarding the underlying atomic data. Wind lines from “super-ionized” ions such as O  VI can, in principle, be used to constrain the distribution of wind-embedded shocks. The new  FASTWIND version v11 is now ready to be used.
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  • aa38464-20
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  • © ESO 2020
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  • ESO
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