Stunted Outbursts and Z Cam–like Behaviors in the Long-term Light Curves of Novalike Cataclysmic Variables

Abstract A program of long-term ground-based photometric monitoring of 134 old novae and novalike cataclysmic variables (CVs) has been concluded. In this paper, we display, analyze, and discuss the light curves of 33 of these targets, which have shown “stunted” outbursts (StOBs) during the years 1990–2014. Because our light curves have long time baselines and strong homogeneity, most of our analysis centers on the aggregate properties of StOBs to take advantage of the strengths of our data sets, as opposed to more detailed analysis of individual systems. The StOBs amplitudes exhibit a range of ∼0.14–1.35 mag, with a peak near ∼0.55 mag and durations in the range of ∼5–50 days. We have provided additional targets including FY Per, X Ser, CT Ser, and BK Lyn. A few Z Cam stars were also monitored, providing a photometric comparison of Z Cam and StOB stars at a common cadence and sampling. We refine the properties of the small StOBs and better characterize their relationship to somewhat similar photometric features in Z Cam–type dwarf novae as well as IW And–type and AH Pic–type phenomena. We also compare our ground-based photometry of four CVs displaying StOBs with results from published Kepler mission photometry. The dense spacing and high precision of the Kepler data reveal faint excursions (dips) that are numerous for some CVs, while the ground-based data cover a wider range of CV types. Ultimately, we find that our data provide evidence for both accretion disk instabilities and rapid mass transfer modulation episodes as probable StOB contributing mechanisms.