An Etymological Dictionary of Astronomy and Astrophysics

A → binary system in which the distance separating the stars is comparable to their size. Most close binaries are spectroscopic binaries (→ spectroscopic binary) and/or eclipsing binaries (→ eclipsing binary). In most of them
→ mass transfer occurs at some stage,
an event which profoundly affects the → stellar evolution of the components. The evolution of close binaries depends on the → initial masses of the two stars and
their → separation. When the more massive star evolves into a → red giant first, material will spill through the inner point onto its companion, thereby affecting its companion’s evolution. Mass transfer can also alter the separation and → orbital period of the binary star.

See also: → close; → binary; → system.