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Astron. Astrophys. 363, 1055-1064 (2000)

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X-ray irradiated model stellar atmospheres

II. Comprehensive treatment of Compton scattering

J. Madej 1 and A. Roz_anska 2

1 Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, PL-00-478 Warsaw, Poland (jm@cirrus.astrouw.edu.pl)
2 Copernicus Astronomical Center, Bartycka 18, PL-00-716 Warsaw, Poland (agata@camk.edu.pl)

Received 15 June 2000 / Accepted 4 October 2000

Abstract

We present equations and details of the computer code for model atmosphere computations, in which we include both nonzero external illumination by very hard X-rays, and Compton scattering opacity and emissivity. We assume both radiative and hydrostatic equilibrium, and LTE equation of state. The code solves simultaneously transfer of thermal radiation emitted by a hot main sequence stellar atmosphere and incident hard X-rays of photon energy approaching electron rest mass.

The equation of radiative transfer and remaining equations of equilibrium contain Compton scattering terms appropriate for scattering of photons of arbitrarily large initial energies. In our paper we consider Compton scattering of photons of energy up to 400 keV on free electrons in fully relativistic thermal motion.

In this paper we consider illumination of a B3 V type star by isotropic X-rays of diluted thermal spectral distribution with temperature [FORMULA] K. Two series of models are computed, hydrogen-helium models and iron rich models. Our results demonstrate, that the external illumination causes extreme temperature rise at least in the uppermost layers. Outgoing spectra exhibit: big UV bump, numerous H, He, and Fe b-f opacity jumps mostly in emission, and also reflected incident spectrum with Compton cut-off. The model spectra also reflect qualitatively spectral properties of the active galactic nuclei (AGN).

Key words: radiative transfer – scattering – stars: atmospheres – galaxies: active

Send offprint requests to: A. Roz_anska

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© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000
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