An Etymological Dictionary of Astronomy and Astrophysics
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The original or model on which something is based or formed.
Something that serves to illustrate the typical qualities of a class.

→ proto-; → type.

A spherical → ionization front of → H II regions that moves radially outward from the → exciting star at a velocity much higher than → sound speed in the surrounding cold neutral gas of uniform density (ahead of the front). R-type ionization fronts corresponds to early evolution of H II regions, and will eventually transform into → D-type ionization fronts. If the motion of the front is supersonic relative to the gas behind as well as ahead of the front, the front is referred to as weak R. The strong R front correspond to a large density increase across the front.

R referring to a rarefied gas; → type; → ionization; → front.

A type of → asteroid containing → pyroxene and → olivine silicates, probably mixed with metallic iron, similar to → stony meteorites. S-type asteroids show high albedo of 0.10-0.22. They include about 17% of known asteroids and occupy the inner → asteroid belt.

S for → stone; → type; → asteroid.

Same as → S star.

S, letter of alphabet; → type; → star.

A group into which stars may be classified according to the characteristics of their spectra. Spectral type correlates with the star's → effective temperature and → color. There are seven main spectral types. From hot and blue to cool and red, they are O, B, A, F, G, K, and M. Each spectral type is divided into several subtypes. For example, from warmest to coolest, spectral type G is G0, G1, G2, G3, and so on to G9. A precise → spectral classification requires determining the → luminosity class. The Sun is spectral type G2 V.

→ spectral; → type.

A special type being part of a more general type, e.g. subtype 2 among G type stars. → subclass.

→ sub-; → type.

The classification of supernovae according to the presence or absence of the absorption lines of different chemical elements that appear in their spectra shortly after their explosion. Basically, supernovae come in two main types: those that have hydrogen (Type II, from a very massive star that blows up) and those that do not (Type I, due to thermonuclear runaways in a less massive star). Both types exhibit a wide variety of subclasses. Type Ia lacks hydrogen and presents a singly-ionized silicon (Si II) line at 6150 Å, near peak light. Type Ib has non-ionized helium (He I) line at 5876 Å, and no strong silicon absorption feature near 6150 Å. Type Ic shows weak or no helium lines and no strong silicon absorption feature near 6150 Å. Type II stars also have various subclasses. See also → Type I supernova, → Type Ia supernova, → Type Ib supernova, → Type Ic supernova, → Type II supernova, → Type II-L supernova, → Type II-n supernova, and → Type II-P supernova

→ supernova; → type.

A group of items that have strongly marked and readily defined similarities.

M.E., from M.Fr., from L. typus "figure, image, form, kind," from Gk. typos "dent, impression, mark, figure, original form," from root of typtein "to strike, beat."

Guné "species; color; form; manner, kind;" Mid.Pers. gônak "kind, species;" Av. gaona- "color; body hair;" PIE base *góur- "(animal) body hair," genitive form *gunós.

A type of → Seyfert galaxy showing both broad and narrow spectral emission lines. The widths of the broad lines indicates velocities around 1000 km s^-1. Sy 1 galaxies are also very bright sources of UV and X-ray emission.

→ type; → one; → Seyfert galaxy.

A type of → Seyfert galaxy showing only narrow emission lines and weak UV and X-ray emissions but strong IR emission.

→ type; → two; → Seyfert galaxy.

A burst of → X-rays observed toward → low-mass X-ray binary (LMXB)s. It is characterized by a sharp increase in → luminosity, which lasts 1-10 s, followed by the peak and a slow decrease, which can last from ~ 10s to 100s. Observationally, X-ray bursts manifest as a bright peak of emission on top of the persistent emission powered by → accretion. See also → Type II burst.

→ type; → burst.

Statistics: An error made if a → hypothesis is rejected when it should be accepted. → Type II error.

→ type; → error.

An → orbital migration of low-mass → planets in which no gap is created in the → protoplanetary disk. According to planetary models, beyond a critical core mass for the forming planet, a gap in the protoplanetary disk is created. The critical mass depends on the mass and → metallicity of the disk and therefore it does not have a singular value, but has been shown to be between about 10-30 Earth masses. Compare with → Type II migration.

→ type; → migration.

A type of supernova whose spectra lacks hydrogen lines. Its → light curve exhibits a sharp maximum with a gradual decrease. Typical magnitudes M_V = -14 to -17. Ejecta velocities about 10,000 km/sec. Type I supernovae have several subtypes: → Type Ia, → Type Ib, and → Type Ic.

Type I initially introduced by R. Minkowski (1941, PASP 53, 224); → type; → supernova.

The → gas tail of of a comet.

→ type; → tail.

A → Type I supernova that presents a singly-ionized silicon (Si II) absorption feature at 6150 Å near peak brightness. Type Ia SNe are believed to result from mass → accretion to a carbon-oxygen → white dwarf in a → close binary system. When the white dwarf mass exceeds the → Chandrasekhar limit, the → degenerate electron pressure can no longer support the accumulated mass and the star collapses in a thermonuclear explosion producing a supernova. The → peak luminosity of SNe Ia is set by the radioactive decay chain ⁵⁶Ni → ⁵⁶Co → ⁵⁶Fe, and the observed photometric correlation between the peak luminosity and the time-scale over which the → light curve decays from its maximum is understood physically as having both the luminosity and → opacity being set by the mass of ⁵⁶Ni synthesized in the explosion. Type Ia supernovae occur in all types of galaxies. Type Ia SNe are used as → standard candles in determining cosmological distances, after normalizing their light curves with the → Phillips relation.

→ type; → supernova.

A → Type I supernova that has neutral helium line (He I) at 5876 Å, and no strong silicon (Si II) absorption feature at 6150 Å. Type Ib supernovae are believed to result from the evolution of → massive stars.

→ type; → supernova.

A → Type I supernova that shows weak or no helium lines and no strong silicon (Si II) absorption feature near 6150 Å. Type Ic supernovae are believed to result from the evolution of → massive stars.

→ type; → supernova.

A burst of → X-rays observed toward → low-mass X-ray binary (LMXB)s and characterized by quick succession of bursts with recurrence intervals as short as ~ 7 s. Type II X-ray bursts look similar to → Type I bursts, but they are thought to be related with spasmodic episodes of → accretion.

→ type; → burst.

Statistics: An error made if a → hypothesis is accepted when it should be rejected. → Type I error.

→ type; → error.