Discovery of a New Dwarf Nova, TSS J022216.4+412259.9: a WZ Sge-type Dwarf Nova Breaking the Shortest Superhump Period Record

We report on the time-resolved CCD photometry of a newly discovered variable star, TSS J022216.4+412259.9 during an outburst in a 2005 November–December brightening. The obtained light curves unambiguously show 0.2–0.3mag modulations, which we confirmed to be the superhump observed among SU UMa-type dwarf novae. We also performed a period search for data obtained during the outburst plateau phase, and revealed the existence of the two periodicities: 0.054868(98)d for thefirst two nights and 0.055544(26)d for the following plateau phase. This bi-periodicity is hardly observed in the usual SU UMa-type dwarf novae, but is characteristic of WZ Sge-type stars. We undoubtedly detected a rebrightening in the post-outburst stage, which is typical of short-period SU UMa-type dwarf novae, including WZ Sge-type stars. These observations suggest that TSS J022216.4+412259.9 may be a new WZ Sge star breaking the shortest superhump period so far of 0.05648d for V592 Her among this class with a known superhump period.