GD 552: a member of the missing post-period-minimum CVs
Cambridge, U.K. ; New York : Cambridge University Press
InIAU Symposium, pp. 70
Article in monograph or in proceedings
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Introduction: GD 552 is a cataclysmic binary which was previously believed to be composed of an M-star and a white dwarf, the latter having an extreme mass of 1.4 solar masses. We show that this is not compatible with new observational evidence and present an alternative model in which the white dwarf has a typical mass and the companion is a brown dwarf, making the system a likely member of the elusive group of CVs which have already evolved through minimum orbital period. Methods: We use spectroscopy (optical at the WHT and ultraviolet at STIS) taken with the aim of detecting emission from the mass donor in this system and modelling the white dwarf properties. Results: We do not detect emission from the previously proposed M star, at a level which allows us to rule out the presence of a near-main-sequence star donor. We find that we can successfully model the system as composed of an ordinary white dwarf and a brown dwarf, at a moderate inclination angle. Discussion: Population synthesis calculations favour the idea that the mass donor reached the stage of brown dwarf through evolution instead of being born as such. This allows us to claim that GD 552 is likely a post-period-minimum CV. There is a key point about our analysis that is worth emphasizing: we have managed to derive particularly strong constraints because of GD 552's relatively long orbital period which maximises the difference between the pre-and post-period-bounce systems. In particular it means that the mass donor in the pre-bounce model is relatively easy to detect, so that failure to detect it makes GD 552 the most secure post-period-minimum CV known.
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