Coordinates (2000.0): R.A.= 20h 03m 15s , Dec. = +58 57’ 19’’ Visual magnitude at maximum = 11.7 Visual magnitude at minimum = 12.5 Period = 194 minutes Ephemerids: M = 2416564.4885 + 0.1349 E
XX Cygni is a short period single pulsating variable star. Usually it is listed among the SX Phoenicis group, but due to its relatively long period of pulsation (compared to the rest of the SX Phe stars) and the large variation amplitude in V, someone consider it belonging to the RR Lyr class. One interesting remark is related to the period variations of these stars: some subtle changes in the period length sometimes occur, probably related with the star’s evolution. But it’s not clear, for example, whether these variations are shortening gradually or in abrupt steps. There are only two dozen of these SX Phe stars known so far, and many of them have been discovered in globular clusters. These stars are mostly giants of spectral type A or F, with absolute magnitudes ranging from 0.0 to +2.0. Their masses range from 1.5 to 2 suns. They are mostly old and metal deficient.
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