Analysis of Three SU UMa-Type Dwarf Novae in the Kepler Field

Abstract

Abstract We studied Kepler light curves of three SU UMa-type dwarf novae: a background dwarf nova of KIC 4378554, V585 Lyr, and V516 Lyr. Both the background dwarf nova and V516 Lyr showed a combination of a precursor and a main superoutburst, during which superhumps always developed in the fading branch of the precursor. This finding supports that the thermal-tidal instability theory explains the origin of superoutburst. A superoutburst of V585 Lyr recorded by Kepler did not show a precursor outburst, and the superhumps developed only after the maximum light: namely, the first-ever example in the Kepler data. Such a superoutburst is understood based on the thermaltidal instability model to be a “case B” superoutburst, discussed by Osaki and Meyer (2003, A&A, 401, 325). From the observation of V585 Lyr, Kepler first clearly revealed the positive period derivative commonly seen in the “stage B” superhumps of dwarf novae with a short orbital period. In all three objects, there was no strong signature of a transition to the dominating stream impact-type component of superhumps. This finding suggests that there is no strong indication of an enhanced mass-transfer following the superoutburst. In V585 Lyr, there were “mini-rebrightenings” with an amplitude of 0.2–0.4 mag and its period of 0.4–0.6d during the period between the superoutburst and the rebrightening. We have determined that the orbital period of V516 Lyr is 0.083999(8)d. In V516 Lyr, some of outbursts were double outbursts with varying degrees. The preceding outburst in the double was of the inside-out nature, while the following one was of the outside-in nature. One of the superoutbursts in V516 Lyr was preceded by a double precursor. The preceding precursor failed to trigger a superoutburst, and the following precursor triggered a superoutburst by developing positive superhumps. We have also developed new methods of reconstructing the light curve of superhumps, and of measuring the times of maxima from poorly sampled Kepler LC data.