We report follow-up observations of the Sloan Digital Sky Survey Cataclysmic Variable SDSS J210014.12+004446.0 ( hereafter SDSS J2100 ) .
We obtained photometry and spectroscopy in both outburst and quiescent states , providing the first quiescent spectrum of this source .
In both states , non-sinusoidal photometric modulations are apparent , suggestive of superhumps , placing SDSS J2100 in the SU UMa subclass of dwarf novae .
However , the periods during outburst and quiescence differ significantly , being 2.099 \pm 0.002 hr and 1.96 \pm 0.02 hr respectively .
Our phase-resolved spectroscopy during outburst yielded an estimate of \sim 2 hr for the orbital period , consistent with the photometry .
The presence of the shorter period modulation at quiescence is unusual , but not unique .
Another atypical feature is the relative weakness of the Balmer emission lines in quiescence .
Overall , we find a close similarity between SDSS J2100 and the well-studied superhump cataclysmic Variable V503 Cygni .
By analogy , we suggest that the quiescent modulation is due to a tilted accretion disk – producing negative superhumps – and the modulation in outburst is due to positive superhumps from the precession of an elliptical disk .