CSS120422:111127+571239: A New SU UMa CV Below the Period Minimum
ATel #4112; P. Garnavich, C. Littlefield (Notre Dame), G. H. Marion, J. Irwin, R. P. Kirshner (CfA), and J. Vinko (U. Szeged)
on 15 May 2012; 20:03 UT
Credential Certification: Peter Garnavich (pgarnavi@gmail.com)
Subjects: Optical, Cataclysmic Variable
We report spectroscopic observations of the optical transient CSS120422:111127+571239 (aka SBS1108+574) which shows superhump oscillations with a period of 0.93 hours (vsnet-alert 14480). Spectra were obtained May 13 and 14 (UT) with the 1.5-m Tillinghast telescope+FAST spectrograph and cover 360-750 nm.
The spectra show a blue continuum with weak features identified as H-alpha in emission and H-beta, H-gamma and H-delta in absorption. HeI at 667.8 and 587.5 nm is also seen in emission. The H-alpha emission is double-peaked with a full width of 2000 km/s.
We conclude CSS120422:111127+571239 is an SU UMa type dwarf nova with an orbital period well below the "period minimum" of 78 minutes (e.g. Littlefair et al. 2007, MNRAS, 381, 827). Typically CVs with orbital periods of less than an hour are helium accreting
AM CVn stars. There do exist a handful of hydrogen accretors below the period minimum (e.g. EI Psc, Thorstensen et al. 2002, ApJ, 567, L49) and the superhump period of CSS120422:111127+571239 suggests it has the shortest orbital period of the class.
