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Astron. Astrophys. 356, 579-584 (2000)

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On the secondary star of the galactic supersoft X-ray source RX J0925.7-4758 and Doppler tomography of the emission lines *

K. Matsumoto 1 and R.E. Mennickent 2

1 Department of Astronomy, Faculty of Science, Kyoto University, Kyoto 606-8502, Japan (katsura@kusastro.kyoto-u.ac.jp)
2 Departamento de Física, Universidad de Concepción, Casilla 160-C, Concepción, Chile (rmennick@stars.cfm.udec.cl)

Received 17 November 1999 / Accepted 11 January 2000

Abstract

We carried out optical spectroscopic observations of the galactic supersoft X-ray source RX J0925.7-4758. The relatively long orbital period among supersoft X-ray sources was confirmed. The nature of the secondary star is discussed using its invisibility in the optical spectrum. Under the hypothesis of a non-eclipsing white dwarf, we derived an A-G giant secondary with an inclination angle of [FORMULA]. Doppler maps of the HeII [FORMULA] and H[FORMULA] emission lines were constructed, which generally resemble those of RX J0019.8+2156, suggesting a common line emitting region in supersoft X-ray sources. The concentration of the main emission region to low-velocities indicates that the mass function gives only a lower limit to the mass of the secondary star.

Key words: accretion, accretion disks – stars: binaries: close – stars: individual: RX J0925.7-4758 – X-rays: stars

* Based on observations obtained at ESO La Silla Observatory (ESO Proposal 61.D-0397).

Send offprint requests to: K. Matsumoto

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© European Southern Observatory (ESO) 2000

Online publication: April 10, 2000
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