Issue |
A&A
Volume 430, Number 2, February I 2005
|
|
---|---|---|
Page(s) | 643 - 654 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361:20034048 | |
Published online | 20 January 2005 |
Model atmospheres and X-ray spectra of bursting neutron stars
II. Iron rich comptonized spectra
1
Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland e-mail: majczyna@camk.edu.pl
2
Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warsaw, Poland
3
Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Received:
3
July
2003
Accepted:
10
August
2004
This paper presents the set of plane-parallel model atmosphere equations
for a very hot neutron star (X-ray burst source). The model equations assume
both hydrostatic and radiative equilibrium, and the equation of state of
an ideal gas in local thermodynamic equilibrium (LTE). The equation of
radiative transfer includes terms describing Compton scattering of photons
on free electrons in fully relativistic thermal motion, for photon
energies approaching . Model equations take into account many
bound-free and free-free energy-dependent opacities
of hydrogen, helium, and the iron ions, and also a dozen bound-bound
opacities for the highest ions of iron. We solve model equations by
partial linearisation and the technique of variable Eddington factors.
Large grid of H-He-Fe model atmospheres of X-ray burst sources has been
computed for
K, a wide range of surface
gravity, and various iron abundances.
We demonstrate that the spectra of X-ray bursters with iron present in
the accreting matter differ significantly from pure H-He spectra
(published in an earlier paper), and also from blackbody spectra.
Comptonized spectra with significant iron abundance are generally closer
to blackbody spectra than spectra of H-He atmospheres.
The ratio of color to effective temperatures in our grid always remains in
the range
.
The present grid of model atmospheres and theoretical X-ray spectra will
be used to determine the effective temperatures, radii and
ratios of
bursting neutron stars from observational data.
Key words: radiative transfer / stars: atmospheres / stars: neutron / X-rays: bursts / stars: magnetic fields / stars: fundamental parameters
© ESO, 2005
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