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

TL;DR

This study analyzes Kepler light curves of three SU UMa-type dwarf novae, confirming aspects of the thermal-tidal instability theory and revealing new behaviors in superoutburst development and superhump evolution.

Contribution

First Kepler observations of multiple SU UMa-type dwarf novae, providing detailed insights into superoutburst mechanisms and superhump period derivatives.

Findings

Support for thermal-tidal instability as the origin of superoutbursts.

First Kepler detection of positive superhump period derivative in short-period systems.

Identification of different superoutburst trigger mechanisms and superhump development patterns.

Abstract

We studied the Kepler light curves of three SU UMa-type dwarf novae. Both the background dwarf nova of KIC 4378554 and V516 Lyr showed a combination of precursor-main superoutburst, during which superhumps always developed on the fading branch of the precursor. This finding supports the thermal-tidal instability theory as the origin of the superoutburst. A superoutburst of V585 Lyr recorded by Kepler did not show a precursor outburst and the superhumps developed only after the maximum light, a first example in the Kepler data so far. Such a superoutburst is understood within the thermal-tidal instability model. The observation of V585 Lyr made the first clear Kepler detection of the positive period derivative commonly seen in the "stage B" superhumps in dwarf novae with short orbital periods. In all objects, there was no strong signature of a transition to the dominating stream impact-type component of superhumps, suggesting that there is no strong indication of an enhanced mass-transfer following the superoutburst. We have determined the orbital period of V516 Lyr to be 0.083999(8) d. In V516 Lyr, some of outbursts were double outbursts in a various degree. The preceding outburst in the double outburst was of the inside-out nature while the following one was of the outside-in nature. One of 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.