Non-LTE model atmosphere analysis of the supersoft X-ray source RX J0122.9-7521

K. Werner1, B.Wolff2, M.W.Pakull3, A.P. Cowley4, P.C. Schmidtke4, J.B.Hutchings5, D. Crampton5

1Universität Potsdam, Lehrstuhl Astrophysik, Germany
2Universität Kiel, Institut für Astronomie und Astrophysik, Germany
3Observatoire Astronomique, Strasbourg, France
4Arizona State University, Department of Physics and Astronomy, Tempe, USA
5Dominion Astrophysical Observatory, Victoria, B.C., Canada

The supersoft X-ray source RX J0122.9-7521 was discovered in the ROSAT all-sky survey and suspected to be a member of the Small Magellanic Cloud (Kahabka etal 1994). More recently the source has been optically identified with an extremely hot PG 1159 star (Cowley etal 1995).

Here we present a NLTE model atmosphere analysis of a pointed ROSAT observation combined with medium resolution optical spectroscopy. RX J0122.9-7521 appears to be the hottest known PG 1159 star. It is compact and relatively massive (Teff=180000 K, log g=7.5, M=0.7 Msun). In contrast to other stars of this group, the carbon and oxygen abundances in the helium-dominated atmosphere of RX J0122.9-7521 are unusually low. Our results allow a distance determination which clearly rules out SMC membership of RX J0122.9-7521.

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