Low states in cataclysmic variables

Cataclysmic variables are usually classified Into dwarf novae, nova-likes, Z Camelopardalis stars, VY Sculptoris stars, and so on, on the basis of their long-term photometric behavior. We show that some aspects of this behavior may be caused by variations in the mass transfer rate from the secondary star about the current secular mean, and the consequent stability or instability of the accretion disk, if present. The most likely cause of the mass transfer variations on these timescales (years or less) is starspots. Mass transfer variations can cause low states in systems with otherwise steady disks, but they produce only subtle effects on dwarf novae, including variations in the outburst shapes and the standstills of Z Cam systems.