symbiotic B[e] star (symB[e])
setâre-ye B[e]-ye hamzi
Fr.: étoile B[e] symbiotique
Fr.: étoile symbiotique
A stellar object whose optical spectrum displays lines characteristic of gases of two very different temperatures, typically of an M star (3500 K) and a B star (20 000 K) superimposed. A symbiotic star is in fact a close binary system.
T Tauri star
Fr.: étoile T Tauri
A member of a class of young stellar objects of roughly 1 solar mass showing strong → infrared excess emission attributed to → circumstellar disks and found within or close to molecular clouds. T Tauri stars are → protostars in the final stages of formation to become a stable → main sequence star. The nuclear reactions in their core have not yet stabilised and the stars are known for the variability of their brightness. See also → classical T Tauri star, → weak-line T Tauri star.
tight star cluster
xuše-ye setâreyi-ye tang
Fr.: amas stellaire serré
A cluster of stars in which members are closely situated so that high resolution observations are required to distinguish them individually.
triggered star formation
diseš-e mâše-yi-ye setâré
Fr.: formation d'étoiles déclanchée
Fr.: étoile triple
A group of three stars visually or physically associated with each other. → triple system.
Fr.: étoile du tournant final de la séquence principale
Fr.: étoile de Tycho
A → supernova of Type Ia in the constellation → Cassiopeia, which Tycho Brahe observed in November 1572. At its peak it was as bright as Venus and was visible in the daytime, reaching a magnitude of about -4. It is now visible as a → supernova remnant about 20 light-years across at a distance of about 7,500 light-years. It is associated with faint emission in the optical and X-rays, but is a strong radio source. Other designations: SN 1572, 3C 10, B Cas, 2U 0022+63.
Named after the Danish astronomer Tycho Brahe (1546-1601), who described the event; → star.
setâre-ye farâbanafš, ~ ultar-banafš
Fr.: étoile ultraviolette
A star, such as O types or hot central stars of planetary nebulae, which radiates essentially in the ultraviolet part of the electromagnetic spectrum.
unclassified B[e] star (unclB[e])
setâre-ye B[e]-ye bi radé
Fr.: étoile B[e] non-classée
A temporary designation for a → B[e] star that cannot be placed in any of the four known classes.
Fr.: étoile non rougie
Ursa Major star cluster
xuše-ye Xers-e Bozorg (#)
Fr.: amas de la Grande Ourse
A moving star cluster containing over 100 stars that are scattered over an area of sky more than 1,000 minutes of arc in diameter. The five brightest stars of the → Big Dipper as well as → Sirius belong to this → dynamical stream.
UX Ori star
setâre-ye UX Šekârgar
Fr.: étoile UX Ori
A star that shows large irregular brightness variations and belongs to the Herbig Ae/Be family, i.e. pre-main sequence stars of intermediate mass. Typically a decrease of 2-3 magnitudes in the visible occurs for a few days to a couple of weeks. Current theories explain this behavior as being an obscuration of the central star by orbiting dust clouds, as well as contribution to the total luminosity by unsteady accretion onto the central star. Also called UXOr.
Fr.: étoile variable
A star whose luminosity changes over periods of time; there are many reasons and many types. → cataclysmic variable; → Cepheid; → pulsating star; → nova; → long-period variable; → short-period variable; → Luminous Blue Variable (LBV); etc.
variable star designation
nâmgozini-ye setâre-ye vartandé
Fr.: designation des étoiles variables
A set of conventions used for naming variable stars. Stars with existing → Bayer designations are not given new designations. Alternatively, the letters R through Z are used followed by the Latin genitive of the name of the hosting constellation. Otherwise, two letters of alphabet are used (334 combinations) with the Latin genitive of the name of the constellation. Finally, the letter V (variable) is used followed by numbers 335, 336, and so on. Some examples are: → P Cygni, → T Tauri, → FU Orionis, → EX Lupi, and V509 Cassiopeiae.
very massive star
setâre-ye besyâr porjerm
Fr.: étoile très massive
violent star formation
diseše surâ-ye setâregân
Fr.: formation violente d'étoiles
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.
Fr.: étoile de type Vz
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).
W Virginis star
setâre-ye W dušizé
Fr.: étoile de type W Virginis
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.
setâre-ye W-R (#)
Fr.: étoile W-R
Short for → Wolf-Rayet star.