An AM CVn star, or AM Canum Venaticorum star, is a type of cataclysmic variable star.
AM CVn stars differ from most other cataclysmic variables (CVs) in the lack of hydrogen lines from their spectra.
AM CVn stars with a white-dwarf donor can be formed when a binary consisting of a white dwarf and a low-mass giant evolve through a common-envelope (CE) phase.
AM CVn stars with a helium-star donor are formed in a similar way, but in this case the giant that causes the common envelope is more massive and produces a helium star rather than a second white dwarf.
The observed rebrightening episodes are similar to those seen during the 2003 June outburst of the AM CVn star V803 Cen.
The AM CVn stars are a class of cataclysmic variables comprising two interacting white dwarfs.
Very few confirmed AM CVn stars are known: only about two dozen are suspected at the time of writing.
Rather few AM CVn stars are known and the characteristics of the outbursting systems are not well studied.