An Etymological Dictionary of Astronomy and Astrophysics
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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.

→ close; → binary; → system.

A binary star system which is composed of a collapsed object (→ degenerate dwarf, → neutron star, or → black hole) in orbit with a low-mass (≤ 0.5 Msol) secondary star, wherein the collapsed star → accretes matter from its → companion. These two objects form a binary system of overall dimensions 10⁶ km with an orbital period of only hours or less. See also: → X-ray binary.

→ compact; → binary; → star; → system.

1) A → binary star system in which the two → components are so close that they exchange gases in a complex manner. Their overlapping → gravitational fields form a "peanut" shaped → equipotential surface.
2) Two roughly similar-sized asteroids or cometary nuclei resting on one another, presumably after coming together very gently. Examples are → Comet 67P/Churyumov-Gerasimenko and the asteroid → (486958) 2014 MU69.

→ contact; → binary.

A system of evolved → binary stars in which both → components have ejected their envelopes and evolve toward → white dwarf stage. So far a half dozen double-degenerate → binary systems are known, for example Henize 2-248 (M. Santander-Garcia et al., 2015, 518, 5).

→ double; → degenerate; → binary; → system.

A → spectroscopic binary in which the → spectral lines of both stars are seen and the lines are alternatively double and single. Same as → SB2 binary. See also: → single-lined binary.

→ double; → line; → binary

A → double-lined spectroscopic binary whose → light curve is typical of an → eclipsing binary.

→ double; → line; → eclipsing; → binary.

Same as → double-lined binary.

→ double; → line; → spectroscopic; → binary.

A binary star in which one of the two stars passes in front of the other so that the system's total light periodically fades. The most famous eclipsing binary is → Algol.

→ eclipse; → binary.

In → stellar dynamics studies of → three-body encounters, a → binary system whose → binding energy far exceeds the → kinetic energy of the relative motion of an incoming third body. In such an encounter, a hard binary is likely to get harder and transfer energy to the incoming star, whereas a → soft binary is likely to be disrupted.

→ hard; → binary.

A member of one of the two main classes of → X-ray binary systems where one of the components is a neutron star or a black hole and the other one a → massive star. HMXBs emit relatively → hard X-rays and usually show regular pulsations, no X-ray bursts, and often X-ray eclipses. Their X-ray luminosity is much larger than their optical luminosity. In our Galaxy HMXBs are found predominantly in the → spiral arms and within the → Galactic disk in young → stellar populations less than 10⁷ years old. One of the most famous HMXB is Cygnus X-1 which was the first stellar-mass black hole discovered. See also: → low-mass X-ray binary.

→ high; → mass; → X-ray; → binary.

A binary star system in which mass transfer between the components takes place. → contact binary; → Roche lobe.

Interacting, adj. of → interact; → binary.

A member of one of the two main classes of → X-ray binary systems where one of the components is a → neutron star or → black hole and the other component a → low-mass star with a spectral type A or later. LMXBs mainly emit → soft X-rays. The ratio of their optical to X-ray luminosities is less than 0.1. They belong to → old stellar populations with ages 5-15 × 10⁹ years and are found in → globular clusters and in the → bulge of our → Milky Way galaxy; some are also found in the disk. Hercules X-1 is an example of LMXBs.
See also: → high-mass X-ray binary.

→ low; → mass; → X-ray; → binary.

A cataclysmic binary in which the white dwarf primary has a strong magnetic field that radically affects the accretion flow in the system. → polar

→ magnetic; → cataclysmic; → binary.

A → close binary system composed of two → massive stars.

→ massive; → close binary star.

A → binary system composed of two → neutron stars.

→ neutron; → star; → binary; → system.

A binary star whose binarity is detectable from its variability and light-curve that has certain specific characteristics.

→ photometric + → binary.

A → binary system whose components are → pre-main sequence stars.

→ pre-; → main sequence; → binary.

Same as → single-lined binary.

SB, for → spectroscopic binary; 1, for → single-lined; → binary.

Same as → double-lined binary.

SB, for → spectroscopic binary; 2, for → double-lined; → binary.

A binary system whose secondary member fills its Roche lobe but whose primary member does not.

→ semi-; detached, p.p. of detach, from O.Fr. destachier (Fr. détacher), from des- "apart," + -tachier (as in atachier "to attach"); → binary.

Dorin, → binary; nim-jodâ, from nim-→ semi- + jodâ "separate," from Mid.Pers. yut "separate, different;" Av. yuta- "separate, apart."