A photometric study of the eclipsing dwarf nova GY Cnc in quiescence and during an outburst

Resumo

The results of photometric observations of the dwarf nova GY Cnc in the Rc filter acquired in 2013–2015 (~3900 orbital cycles, 19 nights in total) are presented, including observations during its outburst in April 2014. The binary’s orbital elements have been refined. The orbital period has changed only insignificantly during the ~30 000P_orb since the earlier observations; no systematic O–C variations were detected, only fluctuations within 0.004^d on time scales of 1500–2000P_orb. A “combined” model is used to solve for the parameters of GY Cnc during two states of the system. The flux from the white dwarf is negligible due to the star’s small size. The temperature of the donor star, T₂ ~ 3667 K (Sp M0.2 V), varies between 3440 and 3900 K (Sp K8.8–M1.7 V). The semi-major axis of the disk is a ~ 0.22a₀, on average. In quiescence, a varies within ~40%. The disk has a considerable eccentricity (e ~ 0.2−0.3) for a < 0.2a₀. The disk shape becomes more circular (e < 0.1) with increasing a. The outburst of GY Cnc was associated with increased luminosity of the disk due to the parameter α_g (related to the viscosity of the disk material) decreasing to 0.1–0.2 and the temperature in the inner parts of the disk increasing twofold, to T_in ~ 95 000 K. These changes were apparently due to the infall of matter onto the surface of the white dwarf as the outburst developed. All parameters of the accretion disk in quiescence display considerable variations about their mean values.