August 11-15, 2014


New results on AM CVn binaries from the SDSS

Philip Carter (University of Warwick)

D. Steeghs (University of Warwick); T. R. Marsh (University of Warwick); B. T. Gaensicke (University of Warwick); E. Breedt (University of Warwick); P. J. Groot (Radboud University Nijmegen); G. Nelemans (Radboud University Nijmegen).

The Sloan Digital Sky Survey (SDSS) has lead to the discovery of 16 ultracompact accreting white dwarf binaries, more than one third of the known population. We have conducted a spectroscopic survey of the region of SDSS colour space occupied by these AM CVn binaries in order to uncover the 'hidden' population in the photometric database. This survey has uncovered significantly fewer new systems than expected, indicating a lower space density than previously predicted. Here we present the latest results from this programme. We use the complete g<=19 part of our survey to calculate a new, lower estimate of the AM CVn binary space density, and present results from our studies of recently discovered systems. These include an AM CVn system that likely has a white dwarf donor, and an unusually helium-rich cataclysmic variable (CV) with an orbital period of 55 minutes. This object is the second example of an AM CVn forming via the often-dismissed evolved CV pathway. The recent discovery of two systems that appear to be following this evolutionary track, suggests that this formation channel may contribute a non-negligible fraction of the total AM CVn population.

Mode of presentation: oral