An Etymological Dictionary of Astronomy and Astrophysics
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A → spectroscopic binary in which only one set of → spectral lines is detectable. The binary nature of the system is deduced from the fact that the spectral lines exhibit periodic → Doppler shifts due to orbital motions in the system. Same as → SB1 binary. See also: → double-lined binary.

→ single; → line; → binary.

In → stellar dynamics studies of → three-body encounters, a → binary system whose → binding energy is smaller than the typical → kinetic energy of the relative motion of an incoming third body. See also → hard binary.

→ soft; → binary.

A binary system that cannot be resolved by a telescope, but can be identified by means of the Doppler shift of the spectral lines. As stars revolve, they alternately approach and recede in the line of sight. This motion is shown up in their spectra as a periodic oscillation or doubling of spectral lines.

→ spectroscopic; → binary.

→ close binary star.

→ tight; → bound system; → binary star.

A → binary system of stars whose components can be resolved telescopically and which have detectable orbital motion.

→ visual; → binary.

A binary system with semi-major axis as large as 10,000 → astronomical units.

→ wide; → binary.

A binary star system where one of the stars has evolved and collapsed into an extremely dense body such as a → white dwarf, a → neutron star, or a → black hole. The enormous gravitational attraction of the massive, dense, but dim component pulls material from the brighter, less massive star in an → accretion disk. The gravitational potential energy of the accreted matter is converted to heat by → viscosity and eventually to high-energy photons in the X-ray range. The brightest X-ray binary is → Scorpius X-1.

→ X-ray; → binary.