The K2 Light Curves and Stunted Outbursts of AC Cnc

Abstract

We describe two observations of the nova-like cataclysmic variable AC Cnc obtained with Kepler during its revamped second mission (K2). Using the K2 1 minute cadence mode, the data were obtained during campaigns 5 and 18. Campaign 5 (C05) lasted from ∼2015 April 27 to ∼2015 July 10, a total of 74.8 days, and yielded ∼106,000 measurements. Campaign 18 (C18) lasted from ∼2018 May 13 to ∼2018 July 2, a total of 50.7 days, yielding ∼72,000 measurements. The C05 light curve reveals two “stunted outbursts” having properties consistent with stunted bursts observed from the ground; a stunted burst was underway during the C18 observation when it ended. During a stunted outburst, the primary eclipse is found to increase in depth, but the residual brightness at the mid-primary eclipse remains nearly constant. By contrast, the secondary eclipse retains the same depth, but the brightness at the mid-secondary eclipse increases during outburst, following the orbital variations of the out-of-eclipse light. The eclipse ephemeris is statistically consistent with historical ephemerides and shows only marginal evidence for a period change. On the basis of the K2 data, we cannot confirm a previously reported non-orbital periodicity in AC Cnc.