Continuous `stunted' outbursts detected from the cataclysmic variable KIC 9202990 using Kepler data

Abstract

Based on early Kepler data, Østensen et al. found that KIC 9202990 showed a 4-h and a two-week photometric period. They suggested the 4-h period was a signature of an orbital period; the longer period was possibly due to precession of an accretion disc and KIC 9202990 was a cataclysmic variable with an accretion disc which is always in a bright state (a nova-like system). Using the full Kepler data set on KIC 9202990 which covers 1421 d (Quarter 2-17), and includes 1-min cadence data from the whole of Quarters 5 and 16, we find that the 4-h period is stable and therefore a signature of the binary orbital period. In contrast, the 10-12 d period is not stable and shows an amplitude between 20 and 50 per cent. This longer period modulation is similar to those nova-like systems which show `stunted' outbursts. We discuss the problems that a precessing disc model has in explaining the observed characteristics and indicate why we favour a stunted outburst model. Although such stunted events are considered to be related to the standard disc instability mechanism, their origin is not well understood. KIC 9202990 shows the lowest amplitude and shortest period of continuous stunted outburst systems, making it an ideal target to better understand stunted outbursts and accretion instabilities in general.