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physical object > natural object > celestial body > star > early star > white dwarf

white dwarf (D, wd)
subject			fact

white dwarf	has symbol D
	has symbol wd
	has definition Faint star lying five or more magnitudes below the main sequence.
	has definition Final stage of a star, at which the nuclear energy is exhausted. Cool, and becoming a dead, black body, it is nevertheless extremely dense.
	has definition A small, faint, dense, dying star that has used up its nuclear fuel and is slowly fading from view. A typical white dwarf has 60 percent of the Sun's mass but is little larger than the Earth. White dwarfs are common, accounting for 10 percent of all stars in the Galaxy; the nearest is Sirius B, just 8.6 light-years away. But no white dwarf is visible to the naked eye.
	has definition Star of high surface temperature, low luminosity, and high density (105-108 g cm-3), with roughly the mass of the Sun and the radius of the Earth, that has exhausted most or all of its nuclear fuel, believed to be a star near its final stage of evolution. When the Sun becomes a white dwarf, its radius will be about 0.01 of its present radius. DA white dwarfs are hydrogen-rich; DB white dwarfs are helium-rich; DC are carbon rich; DF are calcium-rich; DP are magnetic stars. White dwarfs have relatively low rotational velocities.
	has definition Faint very-compact stars at the end of their life. Also used as convenient photometric and flux standards.
	is a kind of early star
early star	has spectral type O, B, A, and early F
star	has star surface temperature
	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 white dwarf :

• DA white dwarf (2 facts) - only strong hydrogen lines present
• DB white dwarf (2 facts) - only strong helium lines present
• DC white dwarf (2 facts) - continuous spectrum, no lines clearly visible
• DO white dwarf (2 facts) - both He and H lines present
• DQ white dwarf (2 facts) - carbon lines (atomic or molecular) present.
• DZ white dwarf (2 facts) - no He nor H lines, but metallic lines present
• Omicron2 Eridani (4 facts) - A triple star that was the first white dwarf ever discovered.
• Sirius B (6 facts) - Companion of Sirius, a white dwarf.
• van Maanen's star (3 facts)

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