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physical object > natural object > celestial body > collection of stars > star system > binary star

binary star
subject			fact

binary star	has number of stars 2
	has orbital period
	has definition A system of two stars orbiting around a common center of gravity. Visual binaries are those whose components can be resolved telescopically (i.e., angular separation > 0'.5) and which have detectable orbital motion. Astrometric binaries are those whose dual nature can be deduced from their variable proper motion; spectroscopic binaries, those whose dual nature can be deduced from their variable radial velocity. At least half of the stars in the solar neighborhood are members of binary (or multiple) systems. (See photometric binaries; optical pairs.)
	is a kind of star
	is a kind of star system
star system	has abundance half the stars in the solar neighborhood are members of star systems
star	has star surface temperature
	has spectral type
	has V magnitude
	has B magnitude
	has U magnitude
	has position on celestial sphere from the point of view of Earth
	has parallax from the point of view of Earth's orbit
	has proper motion
	has radiation at surface which is diffused out from the hotter core
	has energy source gravitational contraction and or fusion
	has energy production which takes place primarily within the core
	has surface density which depends on luminosity class
	has surface temperature greater than 1000 Kelvin
	has apparent magnitude
	has absolute magnitude
	has age
	has catalog star catalog
	has material hydrogen, helium
	has velocity determined from proper motion and radial velocity
	has mass greater than 0.08 the sun's mass
celestial body	has spectra
physical object	has location or center of gravity
	has angular momentum
	has momentum
	has temperature
	has volume
	has extent

Kinds of binary star :

• 17 Leporis (6 facts) - A close binary system (A0 V, M1 III) with a shell-like spectrum indicating that mass transfer may be occurring from the late-type companion onto the A0 primary.
• alpha Centauri (16 facts) (Rigil Kent, HR 5459) - A binary star whose components have G2 V and K5 V spectral types. The nearest star system to the Sun and the third brightest star in the night sky.
• astrometric binary
• Barnard's star (12 facts) - A faint binary star with the second largest proper motion known. Long-term observations of its light curve suggest a possible third component with a mass about 1.2 that of Jupiter, although this observation has been challenged.
• close binary (33 kinds, 149 facts)
• Cygnus X-3 (8 facts) (2U 2030+40) - An X-ray binary. It is also an infrared source, a cosmic ray source, and a strongly variable radio source (interstellar extinction is too high for visible light observations). It is best fitted by a model of an expanding cloud of relativistic electrons emitting synchrotron radiation around a neutron star.
• detached binary (2 facts) - Binary star which is not in contact and in which no significant mass exchange is occurring.
• Kruger 60 AB (7 facts) - A faint dM binary in the Solar neighborhood. It may be a subluminous star.
• Luyten 726-8 (3 facts) - A binary (M5.5e V, M6e V) (component B is UV Cet) with a very small mass (total mass of system (1974) 0.3 M_sun ).
• Mira (15 facts) (omicron Cet) - A red giant that varies in brightness as it pulsates. When brightest, Mira is visible to the naked eye; when dimmest, Mira can be viewed only with optical aid. Mira is the prototype of all pulsating red giants, which are called Miras in its honor., A irregular long-period intrinsic variable. It was named Mira ("wonderful") in 1596 by Fabricius, who made the first recorded observations of its brightness fluctuations. Mira is a double star with a faint B companion which is itself variable.
• Polaris (20 facts) (HR 424, Pole star, North Star) - A supergiant F8 Ib, F3 V visual binary, with an orbital period of thousands of years. The primary (a Cepheid with a pulsation period of 3.97 days) is itself a single-lined spectroscopic double with a period of 29.6 years. There are at least two more faint (12th mag) components of the system.
• RS CVn star (2 facts) - Close binary, which show the HK lines in emission.
• Sirius (16 facts) (alpha CMa, Dog Star, HR 2491) - The brightest star in the sky. Its companion (Sirius B) is a white dwarf of about 0.96 M_sun but only about 0.03 R_sun, the nearest white dwarf to Earth.
• SMC X-1 (6 facts) (2U 0115-73) - An X-ray source in the Small Magellanic Cloud. It is a binary system. Identified with Sanduleak No. 160, a B0 I supergiant (m_v = + 13.6). Because no radial-velocity variations are apparent in Sk 160, the mass of the X-ray emitter must be small relative to Sk 160 (about 2 M_sun if Sk 160 is 20 M_sun), unlike the compact member of CygX-1.
• spectroscopic binary (6 kinds, 49 facts) - Star whose binary nature can be detected from the periodic Doppler shifts of their spectra, owing to their varying velocities in the line of sight. Double-lined spectroscopic binaries have two sets of spectral features, oscillating with opposite phases. Single-lined spectroscopic binaries have only one set of oscillating spectral lines, owing to the dimness of the secondary component. Spectroscopic binaries are typically of spectral type B, with almost circular orbits (whereas long-period M-type binaries have highly eccentric orbits).
• UV Ceti (13 facts) (Luyten 726-8 B) - Late-type dwarf with spectra showing hydrogen emission lines. Faint flare star of very low mass. Like other flare stars, it is a member of a binary system in which both components are of nearly equal brightness. Radio flares have also been observed.
• visual binary (1 kind, 18 facts) - A binary star which can be resolved into two components with current telescopes.
• zeta Aurigae star (2 facts) - Binary star with a K supergiant primary and a main-sequence secondary.

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