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early star
subject			fact

early star	has spectral type O, B, A, and early F
	has definition Hot star of spectral types O, B, A, and early F.
	is a kind of star
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 early star :

• A star (25 kinds, 226 facts) - Star with spectral type A in which the spectrum of the Balmer lines of hydrogen attain their greatest strength. Helium lines can no longer be seen. Some metallic lines are present; in late A stars the H and K lines of ionized calcium appear. A0 stars have a color index of zero.
• B star (30 kinds, 239 facts) - Blue-white star of spectral type B whose spectra are characterized by absorption lines of neutral helium which reach their maximum intensity at B2. The Balmer lines of hydrogen are strong, and lines of singly ionized oxygen and other gases are also present.
• central star of planetary nebula (3 kinds, 10 facts) (planerary nuclei, CPN)
• F star (12 kinds, 135 facts) - Star of spectral type F in which lines of hydrogen and Ca II are of about equal strength. Metal lines also become noticeable.
• luminous blue variable (5 facts) (S Dor variable, Hubble-Sandage variable) - A variable-star designation for the high-luminosity early type objects.
• O star (13 kinds, 78 facts) - Very hot blue star, whose spectra is dominated by the lines of singly ionized helium (see Pickering series). (Most other lines are from at least doubly ionized elements, though H and He I lines are also present.) O stars are useful because they are found in dust clouds and virtually define the spiral arms.
• peculiar star (7 kinds, 25 facts) - Star with spectra that cannot be conveniently fitted into any of the standard spectral classifications. Denoted by a p after spectral type.
• runaway star (3 kinds, 16 facts) - Early type star (O and early B) outside the Galactic plane, which reached large distances (from the Galactic plane) because of their high velocities., Star of spectral type O or early B with unusually high space velocities. Runaway stars are thought to be produced when there is a supernova explosion in a close binary system.
• white dwarf (9 kinds, 33 facts) (D, wd) - Faint star lying five or more magnitudes below the main sequence., Final stage of a star, at which the nuclear energy is exhausted. Cool, and becoming a dead, black body, it is nevertheless extremely dense., 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., 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., Faint very-compact stars at the end of their life. Also used as convenient photometric and flux standards.
• Wolf-Rayet (7 kinds, 43 facts) - Hot stars characterized by wide emission lines of highly ionized elements, standing out distinctly from the continuous spectrum. There exist three varieties: WN, WC and WO, One of a class of very luminous, very hot (as high as 50000 K) stars whose spectra have broad emission lines (mainly He I and He II), which are presumed to originate from material ejected from the star at very high (~ 2000 km s^-1 ) velocities. Some W-R spectra show emission lines due to carbon (WC stars); others show emission lines due to nitrogen (WN stars). (Hiltner and Schild classification: WN-A, narrow lines; WN-B, broad lines.)

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