An Analysis of AAVSO Observations of Z Camelopardalis

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Abstract
We analyze the AAVSO light curve for the cataclysmic variable Z Camelopardalis. The light curve includes 51,086 observations over 67 years. We classify outbursts into three main categories—common, plateau, and anomalous—based on the shape and duration of the outburst. Plateau outbursts are brighter and last longer than common outbursts. Some outbursts end in standstills in which the brightness stays constant roughly 1 mag below maximum light for a few days to 1000 days. The average energy output in a standstill is larger than that during an outburst cycle. All outbursts follow a pattern, the plateau outburst cycle, in which one or more common or anomalous outbursts occur between two plateau outbursts or a plateau outburst and a standstill. Short quiescent durations lead to a higher outburst frequency and more energetic outbursts in intervals dominated by standstills than in other light-curve intervals. Our physical picture for Z Camelopardalis stars follows the standard disk instability mechanism for dwarf novae. The plateau outburst cycle is a series of minor, common "inside out" outbursts that lead to a major, plateau outburst that empties the accretion disk. Standstills occur when the mass transfer rate from the secondary star into the accretion disk surrounding the primary star is too large to produce dwarf nova outbursts. The system resembles a nova-like variable during standstill; it returns to the plateau outburst cycle when the mass transfer rate declines below some critical level. Our analysis suggests that irradiation of the secondary does not play a significant role in the evolution of . Solar-type magnetic cycles are a more plausible mechanism.