SS Cygni star

SS Cygni stars are one of three subclasses of U Geminorum stars (dwarf novae), the others being SU Ursae Majoris stars and Z Camelopardalis stars. Named after the first to be discovered, SS Cygni, these objects undergo well-defined outbursts with an amplitude of 2 to 6 magnitudes, a rise time of 1 to 2 days, and a somewhat longer decline. The mean interval between outbursts ranges from about 10 days to several years. Although most SS Cygni stars display distinct short and long outbursts, the latter are quite different from the supermaxima of SU Ursae Majoris types.