An Etymological Dictionary of Astronomy and Astrophysics
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The concept of star formation pertaining to a variety of systems (OB associations, giant H II regions, H II galaxies, massive star clusters, etc.) that are believed to have formed large numbers of stars in a very short time.

→ violent; → star formation.

A class of → O-type stars whose spectra show He II 4686 absorption line much stronger than any other He line especially He II 4541 or He I 4471. Vz stars are thought to be young stars lying close to the → ZAMS (Walborn & Parker 1992, ApJ 399, L87). Alternatively, the Vz characteristics may be related to the wind properties rather than to the youth of the star (Martins et al., 2005, A&A 441, 735).

V indicating → main sequence, z for "zero age;" → star.

A member of a class of → pulsating stars with a period of 1 to 35 days located in the → instability strip of the → H-R diagram. Also known as type II Cepheid variables, W Virginis stars are typically 1.5 mag fainter than classical Type I Cepheids and have a mass less than that of the Sun. They also exhibit a period-luminosity relation which is distinct, but works in a similar way to the relation for Type I Cepheids. Hence W Virginis stars can also be used to measure Galactic and extragalactic distances.

W, alphabetical letter; → variable star designation; → Virgo; → star.

Short for → Wolf-Rayet star.

→ Wolf-Rayet star.

A stellar catalog which is the world's principal database of astrometric → double star information. It is maintained by the United States Naval Observatory. The WDS Catalog contains positions (J2000), discoverer designations, epochs, position angles, separations, magnitudes, spectral types, proper motions, and, when available, Durchmusterung numbers and notes for the components of 142552 systems (as of Feb 27 2018).

Washington, referring to the location of the United States Naval Observatory in Northwest Washington, D.C; → double; → star; → catalog.

A → WC Wolf-Rayet that its spectrum shows the following emission line characteristics: strong C IV 5801-12 Å, weak or absent C II 4267 Å, and moderate O V 5572-98 Å.

W, from → Wolf-Rayet; C, from → carbon; → star.

A → WC Wolf-Rayet whose spectrum shows the following emission line characteristics: C III 5696 Å very weaker than C IV 5801-12 Å and C III weaker than O V 5572-98 Å.

W, from → Wolf-Rayet; C, from → carbon; → star.

A → WC Wolf-Rayet whose spectrum shows the following emission line characteristics: C III 5696 Å very weaker than C IV 5801-12 Å and C III stronger than O V 5572-98 Å.

W, from → Wolf-Rayet; C, from → carbon; → star.

A → WC Wolf-Rayet with a spectrum shows the following emission line characteristics: C III 5696 Å weaker than C IV 5801-12 Å and C III very stronger than O V 5572-98 Å.

W, from → Wolf-Rayet; C, from → carbon; → star.

A → WC Wolf-Rayet with a spectrum shows the following emission line characteristics: C III 5696 Å stronger than C IV 5801-12 Å, C II 4267 Å absent, and O V 5572-98 Å weak or absent.

W, from → Wolf-Rayet; C, from → carbon; → star.

A → WC Wolf-Rayet whose spectrum shows the following emission line characteristics: C III 569 Å stronger than C IV 5801-12 Å, C II 4267 Å present, and O V 5572-98 Å weak or absent.

W, from → Wolf-Rayet; C, from → carbon; → star.

A member of a class of cntral stars of planetary nebula, → CSPN, which have weaker and narrower emission lines than → Wolf-Rayet-like CSPNe (Tylenda et al. 1993, A&AS 102, 595).

→ weak; → emission; → line.

A T Tauri star that lacks strong emission lines in its optical spectrum, and lacks both strong → stellar wind and → infrared excess. These objects are believed to be → pre-main sequence stars without obvious signs for disk → accretion. Weak-line T Tauri stars result from the evolution of → classical T Tauri stars.

→ weak; → line; → T Tauri star.

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.

An object showing signatures of both → WN Wolf-Rayet stars and → WC Wolf-Rayet stars in the same spectrum, originating from individual stars rather than from WN + WC → binary systems. Such a WN/WC signature implies that the surface composition of the star is → nitrogen and → carbon enriched. This hybrid state results from a mixing process between He-burning → convective core and the overlying nitrogen enriched layers. According to model predictions, this situation corresponds to a short transition phase, lasting 10³ to 10⁴ years, during which a WN star evolves into a WC star. The WN/WC stars so far detected are all of early types.

→ WN Wolf-Rayet; → WC Wolf-Rayet.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N III 4634-4641, 5314 Å as strong as N II 3995 Å, Balmer lines, He I with → P Cygni profile.

W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N II 3995 Å as strong as He II 4686 Å, N III 4634-4641, 5314 Å weak or absent, Balmer lines, He I with → P Cygni profile.

W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N V 4603, 4619 Å weak or absent,He II 4686 Å strong.

W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N V 4603, 4619 Å present, N IV 3479-3484, 4058 Å absent.

W, from → Wolf-Rayet; N, from → nitrogen; → star.

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N IV 3479-3484, 4058 Å very weaker than N V 3479-3484, 4058 Å and N III 4634-4641, 5314 Å weak or absent.

W, from → Wolf-Rayet; N, from → nitrogen; → star.