Continuous `stunted' outbursts detected from the Cataclysmic Variable KIC 9202990 using Kepler data

TL;DR

This study analyzes Kepler data of KIC 9202990, confirming a stable 4-hour orbital period and identifying unstable 10-12 day modulations linked to stunted outbursts, advancing understanding of accretion instabilities in cataclysmic variables.

Contribution

It provides detailed analysis of long-term Kepler data, confirming the orbital period and characterizing the unstable outburst-like modulations, challenging precessing disk models and supporting the stunted outburst hypothesis.

Findings

The 4-hour period is stable, confirming it as the orbital period.

The 10-12 day modulation shows variable amplitude, consistent with stunted outbursts.

KIC 9202990 exhibits the lowest amplitude and shortest period of such systems.

Abstract

Based on early Kepler data, Ostensen et al. (2010) found that KIC 9202990 showed a 4 hr and a two-week photometric period. They suggested the 4 hr period was a signature of an orbital period; the longer period was possibly due to precession of an accretion disk and KIC 9202990 was a cataclysmic variable with an accretion disk which is always in a bright state (a nova-like system). Using the full Kepler dataset 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 hr 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--50 percent. This longer period modulation is similar to those nova-like systems which show `stunted' outbursts. We discuss the problems that a precessing disk 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 disk 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.