The helium-rich cataclysmic variable SBSS 1108+574

P. J. Carter*, D. Steeghs, E. de Miguel, W. Goff, R. A. Koff, T. Krajci, T. R. Marsh, B. T. Gaensicke, E. Breedt, P. J. Groot, G. Nelemans, G. H. A. Roelofs, A. Rau, D. Koester, T. Kupfer

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

17 Citations (Scopus)

Abstract

We present time-resolved spectroscopy and photometry of the dwarf nova SBSS 1108+574, obtained during the 2012 outburst. Its quiescent spectrum is unusually rich in helium, showing broad, double-peaked emission lines from the accretion disc. We measure a line flux ratio He I 5875/H alpha = 0.81 +/- 0.04, a much higher ratio than typically observed in cataclysmic variable stars (CVs). The outburst spectrum shows hydrogen and helium in absorption, with weak emission of Ha and He I 6678, as well as strong He II emission.

From our photometry, we find the superhump period to be 56.34 +/- 0.18 min, in agreement with the previously published result. The spectroscopic period, derived from the radial velocities of the emission lines, is found to be 55.3 +/- 0.8 min, consistent with a previously identified photometric orbital period, and significantly below the normal CV period minimum. This indicates that the donor in SBSS 1108+574 is highly evolved. The superhump excess derived from our photometry implies a mass ratio of q = 0.086 +/- 0.014. Our spectroscopy reveals a grazing eclipse of the large outbursting disc. As the disc is significantly larger during outburst, it is unlikely that an eclipse will be detectable in quiescence. The relatively high accretion rate implied by the detection of outbursts, together with the large mass ratio, suggests that SBSS 1108+574 is still evolving towards its period minimum.

Original languageEnglish
Pages (from-to)372-382
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Volume431
Issue number1
DOIs
Publication statusPublished - May 2013

Keywords

  • accretion, accretion discs
  • binaries: close
  • stars: individual: SBSS 1108+574
  • novae, cataclysmic variables
  • white dwarfs
  • AM CVN STARS
  • MINIMUM ORBITAL PERIOD
  • X-RAY BINARIES
  • WHITE-DWARF
  • WZ SAGITTAE
  • EFFECTIVE TEMPERATURES
  • COMPACT BINARIES
  • ACCRETION DISKS
  • CLOSE BINARIES
  • URSAE MAJORIS

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