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Astron. Astrophys. 318, 108-110 (1997)

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Research Note

Small Magellanic Cloud 13 type supersoft sources

P. Kahabka 1, 2 and E. Ergma 3

1  Astronomical Institute, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
2  Center for High Energy Astrophysics, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
3  Physics Department, Tartu University, Ülikooli 18, EE2400 Tartu Estonia

Received 8 December 1995 / Accepted 26 June 1996


It is proposed that the observational data for the supersoft X-ray source 1E0035.4-7230 in the SMC may be explained in the framework of the standard cataclysmic variable evolution. The fulfilling of several conditions are needed: (1) The white dwarf has a low mass ([FORMULA] 0.6 -0.7 [FORMULA]) and rather thick helium buffer layer on top of the C-O core. (2) After the common envelope phase and before the accretion stage the white dwarf has cooled down ([FORMULA] [FORMULA] [FORMULA] years). (3) After Roche lobe filling when the binary evolution is driven by magnetic braking, the mass accretion rate is [FORMULA] [FORMULA] /yr, the accumulation of the matter at the surface of the cold white dwarf leads to nova outbursts and all accreted matter will be ejected. (4) The accretion will gradually heat up the cool white dwarf and after reaching a steady state equilibrium higher temperature, flashes have become more mild and no longer all accreted matter is lost in the flash. At the current stage we are observing this system after a mild (due to the hot white dwarf condition) hydrogen flash in the phase of residual hydrogen burning. We would like to call this new type of objects SMC 13 type supersoft sources.

Key words: stars: evolution – X-rays: stars – stars:individual 1E 0035.4-7230 (SMC) – Magellanic Clouds

Send offprint requests to: P. Kahabka

© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998