Abstract
We show that the recently discovered short period supersoft source in M31 is probably a progenitor of a magnetic cataclysmic variable (CV). The white dwarf spins asynchronously because of the current high accretion rate. However its fieldstrength is typical of an AM Herculis system, which is what it will ultimately become. We discuss the relevance of this system to CV evolution, and its relation to some particular CVs with special characteristics.
Highlights
A recent XMM-Newton observation of the central region of M31 (Osborne et al 2001) has revealed a supersoft X-ray source XMMU J004319.4þ411758, hereafter M31PSS (1⁄4M31 periodic supersoft) with a coherent period of P 1⁄4 865:5 s
We examine in turn the ideas that the period is orbital, or instead reflects the white dwarf spin
Since the nuclear luminosity of helium-rich accretion is too low to power M31PSS if it is a member of M31, the only remaining way of giving an ultrashort-period system the luminosity required for this is to assume that the accretor is a neutron star or black hole. 4U1820 – 30 is probably a system of this type (Stella, White & Priedhorsky 1987)
Summary
A recent XMM-Newton observation of the central region of M31 (Osborne et al 2001) has revealed a supersoft X-ray source XMMU J004319.4þ411758, hereafter M31PSS (1⁄4M31 periodic supersoft) with a coherent period of P 1⁄4 865:5 s. Periodicities in supersoft sources have all hitherto been straightforwardly interpretable as orbital. The 865.5-s period of M31PSS is so much shorter than the others ðP * 80 min; Greiner 2000) that this interpretation is questionable. We examine in turn the ideas that the period is orbital, or instead reflects the white dwarf spin
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