Fr.: étoiles d'extinction
Stars specifically observed at selected air masses in view of determining the atmospheric extinction coefficients.
extreme HB star
Fr.: étoile EBH
Same as → extreme horizontal branch star.
extreme horizontal branch star (EHB)
setâre-ye šâxe-ye ofoqi-ye ostom
Fr.: étoile de la branche horizontale extrême
The hottest variety of stars on the → horizontal branch with temperatures ranging from 20,000 to 40,000 K. EHB stars are distinguished from normal horizontal branch stars by having extremely thin, inert hydrogen envelopes surrounding the helium-burning core. They are hot, dense stars with masses in a narrow range near 0.5 Msun. These stars have undergone such extreme mass loss during their first ascent up the giant branch that only a very thin hydrogen envelope survives. Stars identified as EHB stars are found in low metallicity globular clusters as an extension of the normal HB.
extremely metal-poor star (EMPS)
stâre-ye ostomâné kamfelez
Fr.: étoile extrêmement faible en métaux
A star with an iron abundance [Fe/H] < -3 found in a → galactic halo. These stars, whose → metallicity is typically less than one thousandth of the solar value, are believed to have formed shortly after the → Big Bang, 13.7 billion years ago. The number of such stars depends on the primordial → initial mass function. If the IMF were steep, there could, in principle, be a lot of EMPSs formed at high → redshifts. Thus many of them could have ended up in the halos of galaxies. See also → Population III star.
extrinsic variable star
setâre-ye vartande-ye borungin
Fr.: étoile variable extrinsèque
A star whose variation in apparent brightness is not due to changes in the star itself but to some external cause, such as eclipsing by a companion.
setâre-ye gune-ye F
Fr.: étoile de type F
A star whose spectrum is characterized by strong → absorption lines of ionized → calcium, Ca II (→ H and K lines), which become much stronger than the hydrogen lines of the → Balmer series. A multitude of fainter metallic lines are also present. Ca II lines strengthen to later types. → Main sequence F stars, of which → Procyon is an example, have a → surface temperature of 6,000 to 7,400°C and a mass of 1.1 to 1.4 → solar masses (Habets & Heintze, 1981, AASS 46, 193).
setâre-ye kamnur (#), ~ nazâr
Fr.: étoile faible
For unaided eye, a star of visual magnitude around 5-6. Otherwise, on an image, a star that has a lesser brightness compared to others of the same field.
Fr.: étoile FHB
Same as → field horizontal branch star.
field horizontal branch star
setâre-ye šâxe-ye ofoqi-ye meydâni
Fr.: étoile de la branche horizontal du champ
A → horizontal branch star with high velocity.
field O star
setâre-ye O-ye meydân
Fr.: étoile O de champ
An → O-type star which is apparently not associated with a → star cluster. A significant fraction of → massive stars in the → Milky Way and other galaxies are located far from star clusters and → star-forming regions. It is known that some of these stars are → runaways, i.e. possess high → space velocities (determined through the → proper motion and/or → radial velocity measurements), and therefore most likely were formed in embedded clusters and then ejected into the field because of dynamical interactions or → binary-→ supernova explosions. However, there exists a group of field O stars whose runaway status is difficult to prove via direct proper motion measurements or whose low space velocities and/or young ages appear to be incompatible with their large separation from known star clusters. The existence of this group led some authors to believe that these stars can form → in situ. The question of whether or not O stars can form in isolation (→ isolated massive star formation) is of crucial importance for → star formation models (Gvaramadze et al., 2012, MNRAS, 424, 3037).
Fr.: étoile de champ
A star that does not belong to a stellar cluster, but happens to be adjacent to it.
Fr.: première étoile
A member of the → Population III → massive stars that formed some 500 Myr after the → Big Bang. First stars had a simple chemical composition consisting only of H, He, and traces of 7Li and were very short-lived. They are the most likely sources of → reionization of the Universe, which put an end to the → Cosmic Dark Age.
setâre-ye barjâ, ~ istâdé, ~ biyâbâni (#)
Fr.: étoile fixe
Setâré, → star; barjâ,
setâre-ye âlâvi, âlâv-setâré
Fr.: étoile à éruption
A member of a class of dwarf stars that undergoes sudden, intense outbursts of light (mean amplitude about 0.5-0.6 mag).
Fr.: étoile fondamentale
A relatively bright star for which coordinates and proper motion have been determined to a very high degree of accuracy.
Fr.: étoile G
A member of a class of stars to which the Sun belongs. The G-type stars on the → main sequence have → surface temperatures of 5,300-6,000 K and therefore appear yellow in color. G type → giant stars (such as → Capella) are almost 100-500 K colder than the corresponding main sequence stars. G type → supergiants have temperatures of 4,500-5,500 K. The spectrum of early type G stars, such as the Sun (G2), is dominated by ionized lines of calcium (→ H and K lines, mainly) and neutral metals. In later type G stars the molecular bands of → CH molecules and → CN molecules become visible. The main sequence and giant stars have masses of ~ 1 solar mass, while the supergiants are of ~ 10 solar masses. The luminosities of G-type giants are almost 30-60 times greater than that of the Sun, whereas the supergiants are 10,000-30,000 times more luminous.
G type star
setâre-ye gune-ye G
Fr.: étoile de type G
A yellowish star whose surface temperature is about 6000 K and its spectrum is dominated by H and K lines of ionized calcium (Ca II 3968 Å and 3934 Å).
setâre-ye gune-ye G
Fr.: étoile de type G
Same as → G star.
Fr.: étoile Grenat
A variable → red supergiant star of → spectral type M2 Ia in the → constellation → Cepheus. Also called → Mu Cephei. Its → apparent magnitude is usually about 4.5 and varies from 3.6 to 5.1. It is also a → triple star.
Garnet "a deep-red color," from the more or less transparent, usually red, silicate mineral that has a vitreous luster. So named by William Herschel from its unusual deep reddish tint. From O.Fr. grenat "garnet," from M.L. granatum, originally an adj., "of dark red color," probably abstracted from pomegranate, from M.L. pomum granatum "apple with many seeds," from pome "apple, fruit" + grenate "having grains."
Nârsang, from nâr, from anâr "pomegranate," from Mid.Pers. anâr "pomegranate" + sang, → stone.
setâre-ye qulpeykar (#)
Fr.: étoile géante