  AU Pegasi is a pulsating star in a spectroscopic binary system with an
orbital period of 53.26 days. Between 1960 and 1990 an extremely rapid period
increase was observed in the value of the pulsation period, but in the last 15
years the observation show that the period set in 2.411 days. Fourier analysis
of photometric data obtained during the ASAS project and those taken at the
Piszkesteto Mountain Station of the Konkoly Observatory during 1994-2005
indicate that AU Pegasi is pulsating in two modes simultaneously, and the ratio
of the frequencies of the two modes is 0.706, a value common for double-mode
classical Cepheids. A careful analysis of other photometric observations
obtained during the era of the strong period increase also revealed existence
of a second mode. This may suggest that this star is not a Type II Cepheid,
despite its galactic position.
