The activity of the dwarf nova RU Pegasi with rapidly changing outburst types

Abstract

ABSTRACT RU Pegasi is a dwarf nova (DN) of the U Geminorum type. This analysis of its long-term optical activity uses data from the data base of the American Association of Variable Star Observers (AAVSO). It concentrates on investigating the properties of the individual outbursts and the time evolution of the ensemble of these events. No significant irradiation of the disc by the white dwarf was detected. In the interpretation, a variable steepness of the rising branches of the individual outbursts shows that the start of outbursts of RU Peg can occur at various distances from the disc centre without remarkable changes of the outburst recurrence time TC. The disc overflow of the inflowing mass stream, varying with time, could contribute to the changes in the starting position of the heating front, and hence the variations of the outburst types. A typical length of TC was 90 d. The segments of the relatively stable length of TC were accompanied by the primarily little variable and small values of the fluence (the energy radiated in the optical band in the individual outbursts). Jumps of TC, accompanied by the big scatter of the fluences, sometimes replaced them. In the interpretation, a combination of variations of TC with the unstable properties of the outbursts, including an unstable mass transfer rate between the components, shows the influence of several mechanisms on the state of the disc in various time segments.