Journal Article

CSS100603:112253−111037: a helium-rich dwarf nova with a 65 min orbital period

E. Breedt, B. T. Gänsicke, T. R. Marsh, D. Steeghs, A. J. Drake and C. M. Copperwheat

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 425, issue 4, pages 2548-2556
Published in print October 2012 | ISSN: 0035-8711
Published online October 2012 | e-ISSN: 1365-2966 | DOI:
CSS100603:112253−111037: a helium-rich dwarf nova with a 65 min orbital period

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We present time-resolved optical spectroscopy of the dwarf nova CSS100603:112253−111037. Its optical spectrum is rich in helium, with broad, double-peaked emission lines produced in an accretion disc. We measure a line flux ratio He i λ5876/Hα = 1.49 ± 0.04, a much higher ratio than is typically observed in dwarf novae. The orbital period, as derived from the radial velocity of the line wings, is 65.233 ± 0.015  min. In combination with the previously measured superhump period, this implies an extreme mass ratio of M2/M1 = 0.017 ± 0.004. The Hα  and He i λ 6678 emission lines additionally have a narrow central spike, as is often seen in the spectra of AM CVn-type stars. Comparing their properties with cataclysmic variables (CVs), AM CVn systems and hydrogen binaries below the CV period minimum, we argue that CSS100603:112253−111037 is the first compelling example of an AM CVn system forming via the evolved CV channel.

With the addition of this system, evolved CVs now account for 7 per cent of all known semidetached white dwarf binaries with Porb < 76 min. Two recently discovered binaries may further increase this figure. Although the selection bias of this sample is not yet well defined, these systems support the evolved CV model as a possible formation channel for ultracompact accreting binaries. The orbital periods of the three ultracompact hydrogen accreting binaries overlap with those of the long-period AM CVn stars, but there are currently no known systems in the period range of 67–76  min.

Keywords: binaries: close; stars: dwarf novae; stars: individual: CSS100603:112253− 111037; novae, cataclysmic variables

Journal Article.  6994 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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