An Etymological Dictionary of Astronomy and Astrophysics
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The → orbital migration of forming → planets that → accrete enough disk material to exceed the critical mass. This type migrates in a gap created in the → protoplanetary disk. Compare with → Type I migration.

→ type; → migration.

A supernova type whose spectrum contains hydrogen lines. Compared with → Type I supernovae, its → light curve has a broader peak at maximum and dies away more rapidly. The magnitudes are smaller, ranging from M_V = -12 to -13.5, and the ejecta have lower velocities (about 5,000 km/sec). These supernovae, which result from the final evolution of → massive stars, have three main divisions: → Type II-P, → Type II-L, and → Type II-n.

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

The → dust tail of a → comet.

→ type; → tail.

A → Type II supernova which displays a linear decrease in its → light curve.

→ Type II supernova; L short for → linear.

A → Type II supernova which shows intermediate or very narrow width hydrogen → emission lines in the spectra.

→ Type II supernova; n short for → narrow.

A → Type II supernova which reaches a plateau in its → light curve. The vast majority of Type II SNe are characterized by a fast (few days) rise to a flat light curve, most pronounced in the reddest optical bands, with a duration of 80-100 days. This plateau phase is interpreted as the recession of the photosphere as the ejecta expand and cool. The spectra of SNe II-P are typically dominated by strong → P Cygni profiles of hydrogen lines, as well as iron absorption features (for a review, e.g., see Filippenko 1997, ARA&A 35, 309).

→ Type II supernova; P short for → plateau.

A → main sequence → O star with low luminosity and surprisingly weak → stellar wind compared to "classical" dwarfs. The → mass loss rates are lower than 10^-8 solar masses per year and the → modified wind momenta nearly 2 orders of magnitude smaller than that expected from wind models for typical O stars. Weak-wind O-type stars occur in both → metal-rich and → metal-poor environments. Their nature is not yet fully understood. same as → weak wind problem.

→ weak; → wind; → O-type star.

A → WN Wolf-Rayet star which is hydrogen rich. WNh stars are initially more massive and have lost relatively little mass compared to other WR stars. It is suggested that these types are core hydrogen burning → main sequence objects. The most massive stars currently known are all WNh stars rather than O-type main sequence stars.

WN, from → WN Wolf-Rayet; h, from → hydrogen.

An oxygen-rich → Wolf-Rayet star whose spectrum shows the following emission line characteristics: No O IV 3400 Å, strong O VI 3811-34 Å, O V 5572-98 Å about or stronger than C IV 5801-12 Å, no C III 5696 Å.

W, from → Wolf-Rayet; O, from → oxygen; → star.

An oxygen-rich → Wolf-Rayet star whose spectrum shows the following emission line characteristics: No O IV 3400 Å, strong O VI 3811-34 Å, O V 5572-98 Å weaker than C IV 5801-12 Å, no C III 5696 Å.

W, from → Wolf-Rayet; O, from → oxygen; → star.