bimodal star formation
diseš-e domod-e setâregân
Fr.: formation bimodale d'étoile
A concept of → star formation in which → high-mass stars and → low-mass stars form in different physical conditions involving different → molecular clouds. Following the pioneering suggestion of Herbig (1962), successive investigations have generally supported the idea that star formation proceeds bimodally with respect to stellar mass. The star formation rate appears to differ both spatially and temporally for low mass and → massive stars. This is of considerable importance for galactic evolution, since the low-mass stars lock up mass and are long-lived, low luminosity survivors to the present epoch, whereas massive stars are short-lived, recycle and enrich interstellar gas, and leave dark remnants while producing a high luminosity per unit of mass (Silk, J., 1988, in Galactic and Extragalactic Star Formation, p. 503, eds. R. E. Pudritz and M. Fich).
Fr.: étoile binaire
→ binary; → star.
Fr.: étoile à effet Blazhko
A star showing the → Blazhko effect.
blue halo star
setâregân-e âbi-ye hâlé
Fr.: étoiles bleues du halo
blue HB star
Fr.: étoile BHB
Same as → blue horizontal branch star.
blue hook star
setare-ye qollab-e abi
Fr.: étoile du crochet bleu
A rare class of → horizontal branch (HB)
stars that so far have been
found in only very few Galactic → globular clusters.
These stars are such called because they
form a blue hook at the hot end of the HB in
→ far ultraviolet
(FUV) → color-magnitude diagrams.
The physical mechanism that produces blue hook populations
is still uncertain. At least two scenarios have been proposed.
blue horizontal branch star
setâre-ye âbi-ye šâxe-ye ofoqi
Fr.: étoile bleue de la branche horizontale
A member of a population of blue stars appearing on the → horizontal branch in the → Hertzsprung-Russell diagram of the Galactic → halo populations and → globular clusters. Belonging to → spectral types B3 to A0, they have evolved past the → red giant stage and are burning helium in their core.
born-again AGB star
setâre-ye AGB-ye bâzzâdé
Fr.: étoile AGB recyclée
A → post-AGB star that undergoes a last → thermal pulse when it is already on the → white dwarf → cooling track. The thermal pulse will expand the hot central star, whereby hydrogen will be ingested into the → helium burning shell. This will temporarily return the star to the → AGB phase it has previously left.
Fr.: étoile Bq
burst of star formation
belk-e diseš-e setâregân
Fr.: flambée de formation d'étoiles
An intense → star formation activity in a region of → interstellar medium or, more globally, in a → galaxy. It is characterized by a → star formation rate which is much higher than the corresponding average. Same as → starburst.
Fr.: étoile B[e]
A → Be star with → forbidden lines in emission in its spectrum. B[e] stars show large → infrared excess due to → circumstellar dust emission. See also → supergiant B[e] star, → pre-main sequence B[e] star, → compact planetary nebula B[e] star, → symbiotic B[e] star, and → unclassified B[e] star.
B, referring to the spectral type; e for emission lines, brackets for distinction from Be; → star.
Fr.: étoile carbonée
carbon-enhanced metal-poor star (CEMP)
setâre-ye kamfelez-e karbon bolandidé
Fr.: étoile pauvre en métaux enrichie en carbon
A star that presents very low → iron → abundances [Fe/H] < -4 but an → anomalous richness in carbon. CEMP stars have been defined as a subset of → metal-poor stars that exhibit elevated [C/Fe] ≥ +1.0. It has been recognized that ~15-20% of stars with [Fe/H] < -2.0 are carbon enhanced. This fraction rises to 30% for [Fe/H] < -3.0, to 40% for [Fe/H] < -3.5, and ~75% for [Fe/H] < -4.0. This increasing trend of CEMP-star frequency with declining [Fe/H] is confirmed by the observation of many thousands of CEMP stars (Daniela Carollo + ApJ 2014, 788, 180). See also → extremely metal-poor star (EMPS)
chemically peculiar star
setâre-ye šimikâné afd
Fr.: étoile chimiquement particulière
A → main sequence star of
→ spectral type A or B
(→ A-type star, → B-type star)
identified by the presence of anomalously strong or weak
→ absorption lines of certain elements
in their spectra.
CP stars have been divided into four main classes on the basis of their
spectra: 1) non-magnetic metallic-lined (CP1,
→ Am star), magnetic (CP2,
→ Ap star), non-magnetic mercury-manganese (CP3,
→ HgMn star), and
helium-weak (CP4, → He-weak star).
setâre-ye pirâqotbi (#)
Fr.: étoile circumpolaire
Star that, from a given observer's → latitude, does not rise or set, but circles around the → celestial pole. To be circumpolar, a star must have a polar distance that is less than the observer's latitude. Whether a given star is circumpolar at the observer's latitude (φ) may be calculated in terms of the star's → declination (δ). The star is circumpolar if φ + δ ≥ +90° (observer in northern hemisphere), or φ + δ ≤ -90° (observer in southern hemisphere).
classical T Tauri star
setâre-ye T-Gâv-e kelâsik
Fr.: étoile T Tauri classique
A → T Tauri star in which → accretion from a → circumstellar disk is responsible for ultraviolet and infrared excess emission and for a moderate to strong emission line spectrum superimposed on the photospheric spectrum. Classical T Tauri stars probably evolve into → weak-line T Tauri stars when their disks are fully accreted by the stars.
close binary star
setâre-ye dorin-e kip
Fr.: étoile binaire serrée
A binary system in which the separation of the component stars is comparable to their diameters, so that they influence each other's evolution most commonly by the tidal forces.
Fr.: étoile CNO
Fr.: étoile dans son cocon
A star hidden in a dense envelope of gas and dust which is a strong source of infrared emission.
Fr.: étoile effondrée
A star that has undergone → collapse.