Serendipitous Kepler observations of a background dwarf nova of SU UMa type

TL;DR

This paper reports the discovery and detailed observation of a background SU UMa-type dwarf nova in Kepler data, revealing its outburst behavior, superhump period, and transition in accretion dynamics over 22 months.

Contribution

It provides the first detailed Kepler-based analysis of a background dwarf nova, including outburst patterns and superhump characteristics, enhancing understanding of their frequency and behavior.

Findings

Observed five outbursts including a superoutburst

Superhump period measured at 1.842 hours

Transition from disc-dominated to mixed superhump signals

Abstract

We have discovered a dwarf nova (DN) of type SU UMa in Kepler data which is 7.0 arcsec from the G-type exoplanet survey target KIC 4378554. The DN appears as a background source in the pixel aperture of the foreground G star. We extracted only the pixels where the DN is present and observed the source to undergo five outbursts -- one a superoutburst -- over a timespan of 22 months. The superoutburst was triggered by a normal outburst, a feature that has been seen in all DNe superoutburst observed by Kepler. Superhumps during the super outburst had a period of 1.842+/-0.004 h and we see a transition from disc-dominated superhump signal to a mix of disc and accretion stream impact. Predictions of the number of DNe present in Kepler data based on previously published space densities vary from 0.3 to 258. An investigation of the background pixels targets would lead to firmer constraints on the space density of DN.