Theoretical X-ray spectra of hot H-rich white dwarfs. Impact of new partition functions of iron, Fe V through Fe VII

Details Theoretical X-ray spectra of hot H-rich white dwarfs. Impact of new partition functions of iron, Fe V through Fe VII Theoretical X-ray spectra of hot H-rich white dwarfs. Impact of new partition functions of iron, Fe V through Fe VII

Mar 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999a%26a...343..531m&link_type=abstract

Astronomy and Astrophysics, v.343, p.531-535 (1999)

Astronomy and Astrophysics

Astrophysics

2

Atomic Data, Stars: Atmospheres, Stars: White Dwarfs, X-Rays: Stars

Scientific paper

{ In this paper we discuss new method for the atomic partition function (APF) computations, which is then applied to highly ionized iron, Fe V through Fe VII. Subsequently we have computed LTE model atmospheres of two hydrogen-rich white dwarf stars of the effective temperatures T_eff = 8 x 10(4) K and 1.2 x 10(5) K, and log g = 8.0 (cgs units), which included trace abundance of iron. Both models correspond to the hottest DA white dwarfs observed e.g. by ROSAT and EUVE missions in the extreme UV and X-rays, in which stars H-rich atmospheres contain small amount of metals driven outwards by radiation pressure. Computational results exhibit a significant impact of the new partition functions of Fe V through Fe VII on both the iron ionization stratification in analysed atmospheres, and their theoretical X-ray opacities and spectra. We conclude, that in both stars our improved APF predict increase of their EUV and X-ray luminosities by factors of 3 to 10, as compared with models based on previously published iron partition functions. We demonstrate also the importance of our APF on luminosity ratio s2/s1 in both EUV filters of the Wide Field Camera (ROSAT) in case of the hotter, Fe-rich white dwarf of T_eff = 1.2 x 10(5) K.

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