subhumps

Subhumps are periodic variations in the brightness of a cataclysmic variable star, typically observed in dwarf novae and some nova-like variables. They are distinct from the main hump, which is caused by the tidal distortion of the secondary star by the primary white dwarf. Subhumps are believed to be caused by the precession of the accretion disk around the white dwarf, which can be influenced by the gravitational pull of the secondary star.

The period of subhumps is usually slightly longer than the orbital period of the binary system, typically by a few percent. This difference is attributed to the fact that the disk precesses around the white dwarf, which is itself orbiting the secondary star. The amplitude of subhumps can vary, but they are usually smaller than the main hump.

Subhumps were first observed in the 1970s and have since been studied extensively. They provide valuable information about the structure and dynamics of accretion disks in cataclysmic variable stars. The study of subhumps has also led to the development of theories about the nature of the accretion process in these systems.