An Etymological Dictionary of Astronomy and Astrophysics
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A small class of evolved → massive stars showing spectral properties intermediate between those of → Of star and → WN Wolf-Rayet stars. Several of them have been found to possess non-spherical nitrogen-rich circumstellar nebulae. Ofpe/WN9 stars are considered to be transition objects between Of and W-R stars. This type of stars was first identified by Walborn (1982), who introduced the classification Ofpe/WN9, indicating that the stars could not be classified solely as Of stars, nor as WNL stars. Ofpe/WN9 stars have been found in the → Milky Way, the → Large Magellanic Cloud, → M31, and M33. Currently 10 Ofpe/WN9 stars are known in the LMC. Observational evidence suggests a close relationship between the class of → LBVs and the Ofpe/WN9 stars. A notable example is the prototype Ofpe/WN9 star R127 in the LMC that became an LBV on a time-scale of the order of a year. The possibility of such a relationship has been explored by Smith et al. (1994), who proposed that some LBVs show spectral morphologies that make them appear as an extension of the WN sequence toward later spectral types. Hence, they reclassified Ofpe/WN9 stars as WN10-11.

Ofpe, from → Of star; p for "peculiar;" e refers to the presence of other emission lines in addition to the Of ones, mainly H and He I, although also Si III. This peculiar class in the LMC was first described by Walborn (1977, ApJ 215, 53), where he called them "O Iafpe extr" based on the most similar Galactic objects known at that time. Subsequently Walborn (1983, ApJ 256, 452) and Bohannan & Walborn (1989, PASP 101, 520) suggested an extension of the WN sequence and/or transition between Of and WN. This nomenclature Ofpe/WN9 has been rather widely adopted. Later on, Smith et al. (1994) broke the Ofpe/WN9 and related Galactic types into WN10-11 subtypes to include this group of emission line stars.

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.

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.

A new type of → Wolf-Rayet stars found in the → Large Magellanic Cloud (LMC). These stars have both strong → emission lines, as well as → He II lines and → Balmer lines in absorption and spectroscopically resemble a → WN3 and → O3V binary pair. However, they are visually too faint to be WN3+O3 V → binary systems. So far nine WN3/O3 types have been detected, making up ~ 6% of the population of LMC WRs. Their temperatures are estimated to be around 100,000 K, a bit hotter than the majority of → WN Wolf-Rayet stars (by around 10,000 K) although a few hotter WNs are known. The abundances are what you would expect for → CNO equilibrium. However, most anomalous are their → mass-loss rates which are more like that of an → O star than a WN star. While their evolutionary status is uncertain, their low mass-loss rates and → wind velocities suggest that they are not products of homogeneous evolution. It is possible instead that these stars represent an intermediate stage between O stars and WNs. Since WN3/O3 stars are unknown in the Milky Way, their formation would depend upon → metallicity (Neugent et al., 2017, arxiv:1704.05497).

→ WN3; → O3; → star.

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

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N III 4634-4641, 5314 Å as strong as N IV 3479-3484, 4058 Å as strong as N V 3479-3484, 4058 Å.

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

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N III 4634-4641, 5314 Å about N IV 3479-3484, 4058 Å and N V 3479-3484, 4058 Å present, but weak.

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

A → WN Wolf-Rayet star whose spectrum shows the following emission line characteristics: N III 4634-4641, 5314 Å stronger than N IV 3479-3484, 4058 Å, N III weaker than He II 4686 Å, He I weak 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 III 4634-4641, 5314 Å very stronger than N IV 3479-3484, 4058 Å, N III about He II 4686 Å, and 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 III 4634-4641, 5314 Å stronger than N II 3995 Å, N IV 3479-3484, 4058 Å absent, He I with → P Cygni profile.

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

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.

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.

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.