An Etymological Dictionary of Astronomy and Astrophysics
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A → Wolf-Rayet star whose spectrum is dominated by emission lines of ionized carbon: C III 5696 Å, C III / C IV 4650 Å, C IV 5801-12 Å. This type is divided in sub-types WC4 to WC9.
For theoretical models, a Wolf-Rayet star whose carbon abundance at surface is larger than nitrogen abundance and has the abundance ratio (C + O) / He < 1 (in number).

W short for Wolf-Rayet star, C for → carbon.

A → Wolf-Rayet star whose spectrum is dominated by emission lines of ionized nitrogen: N II 3995 Å, N III 4634-4661 Å, N III 5314 Å, N IV 3479-3484 Å, N IV 4058 Å, N V 4603 Å, N V 4619 Å, and N V 4933-4944 Å. This type is divided in sub-types WN2 to WN11.

W short for Wolf-Rayet star, N for → nitrogen.

In theoretical models, a → Wolf-Rayet star without hydrogen at its surface (< 10^-5 in number) and with surface carbon abundance smaller than nitrogen abundance.

W short for Wolf-Rayet star, N for → nitrogen, E for early.

In theoretical models, a → Wolf-Rayet star with hydrogen at its surface (> 10^-5 in number). A star enters the Wolf-Rayet phase as a WNL, then may evolve through the sequence WNL → WNE, → WC, → WO. It can end its evolution at any of these stages.

W short for Wolf-Rayet star, N for → nitrogen, L for late.

A → Wolf-Rayet star whose spectrum shows emission lines of carbon and strong emission lines of oxygen O VI 3811-34 Å. In theoretical models, a W-R star whose carbon abundance at surface is larger than nitrogen abundance and has the abundance ratio (C + O) / He > 1 (in number).

W short for Wolf-Rayet star, O for → oxygen.

A subset of → starburst galaxies whose integrated spectra show broad emission features attributed to the presence of hundreds to thousands → Wolf-Rayet stars. The most massive stars formed in the burst evolve rapidly into a substantial population of Wolf-Rayet stars in aggregations of ionized gas.

→ Wolf-Rayet star; → galaxy.

A type of very luminous, very hot (as high as 50,000 K) stars whose spectrum is characterized by 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. The most massive → O stars (M > 25 → solar masses for → solar metallicity) become W-R stars around 2 and 3 million years after their birth, spending only some few hundreds of thousands of years (≤ 10⁶ years) in this phase until they explode as → type Ib and → type Ic supernovae. The minimum stellar mass that an O star needs to reach the W-R phase and its duration is dependent on → metallicity. → WC Wolf-Rayet; → WNE Wolf-Rayet; → WNL Wolf-Rayet; → WO Wolf-Rayet. For a review see: P. A. Crowther, 2007, Annu. Rev. of Astron. Astrophys. 45, 177.

Named after the French astronomers Charles Wolf (1827-1918) and Georges Rayet (1839-1906), of the Paris Observatory. In 1867 they discovered three stars in the constellation Cygnus (now designated HD191765, HD192103, and HD192641), that displayed broad emission bands in their spectra; → star.