The dwarf nova V1239 herculis in quiescence

Abstract

The results of a study of the integrated brightness of the SU UMa eclipsing binary V1239 Her are presented. The systemwas monitored on nine nights in 2013–2014 when the binary was in quiescence. The orbital period is refined (Porb = 0.100082222(2)d) and the system’s light curves obtained. These curves provide evidence for active processes in the system between outbursts: the depths of both minima and the amplitude of the pre-eclipse hump vary, and one of the light curves exhibits no hump at all. The parameters of the accretion disk, hot spot, and gas stream in V1239 Her for several epochs are determined in a “combined” model taking into account the contributions to the total radiation flux from the opaque part of the gas stream and the hot spot on the lateral surface of the disk. Lower limits for the time scale for variations of the disk characteristics are estimated: the viscosity parameter (αg), temperature of the inner parts of the disk (Tin), and thickness of the outer edge of the disk (βd). These can vary appreciably over less than 10 orbital cycles. In the model used, the solution for the light curve that lacks a pre-eclipse hump (JD 2456746) implies the absence of a hot spot on the disk’s lateral surface: the radius of the spot is negligible, and temperatures of the spot and at the base of the gas stream are lower than those obtained for the other light curves. The disappearance of the hot spot is accompanied by an abrupt decrease in the disk radius and αg, as well as a decrease in the thickness of the disk’s outer edge. A comparison with the system’s parameters derived from the light curve for the previous observation date (JD 2456718) suggests that the disk mass decreased significantly between these two dates (∼280Porb); this decrease could be due to a reduced outflow rate from the secondary, as well as the possible infall of a considerable fraction of the matter from the disk onto the surface of the white dwarf.