Fr.: couche super-eddingtonienne
In some stellar models, particularly for evolved → massive stars, such as → red supergiants, → Luminous Blue Variables, and → Wolf-Rayet stars, an outermost layer of the stellar envelope where the luminosity might exceed the → Eddington limit. This is due to the → opacity peak produced by the variation in the ionization level of hydrogen in the outer → convective envelope, beneath the surface, of very luminous stars. The opacity peak generates supra-Eddington layers and density inversion. The high opacity decreases the Eddington luminosity in these layers, possibly to fainter levels than the actual stellar luminosity. As a result, the → radiative acceleration exceeds the → gravitational acceleration leading to → mass loss enhancement (see, e.g., A. Maeder, Physics, Formation and Evolution of Rotating Stars, Springer, 2009).
supra-horizontal branch star
setâre-ye farâz-e šâxe-ye ofoqi
Fr.: étoile au-dessus de la branche horizontale
A member of a rare class of objects found in → globular clusters to lie about one magnitude above and to the blue part of the → horizontal branch. These stars are identified as post → EHB stars on their way from to the → asymptotic giant branch.
1) Highest in rank or authority.
M.E., from M.Fr. suprême, and directly from L. supremus "highest," superlative of superus "situated above," from super "above," → super-.
Fr.: rayon de balayage
The → radius of a → supernova remnant (SNR) when, at the end of the → free expansion phase, the mass of the swept-up → shell equals that of the ejected gas from the → supernova explosion. It is given by RSW = (3Me / 4πρ0)(1/3), where Me is the ejected mass and ρ0 is the initial density of the → interstellar medium.
Fr.: groupe de symétrie
A group of symmetry-preserving operations composed of all rigid motions or similarity transformations of some geometric object onto itself.
Fr.: support thermique
In star formation models, the gas pressure that counters the collapsing pull of gravity.
Electrical circuit consisting of two dissimilar metals, in which an electromotive force is produced when the two junctions are at different temperatures.
Fr.: supernova thermonucléaire
Same as → type Ia supernova
Fr.: troisième dragage
A → dredge-up process that occurs in the stellar interior during He shell burning, as in → asymptotic giant branch (AGB) stars. These stars consist of a degenerate carbon-oxygen core, surrounded by a helium-rich region, above which lies a hydrogen-rich convective envelope. Following thermal pulses of the helium-burning shell, the convective envelope moves inward in mass, penetrating the hydrogen-exhausted regions. This is known as third dredge-up. As convection moves inward, nuclear processed materials are carried to the surface.
jafsari-ye kešandi, jofteš-e
Fr.: couplage par marées
In a system composed of one celestial body orbiting another, the synchronization of the orbital and rotational motions of the two bodies under the action of → tidal forces. For example, Pluto is tidally coupled to its moon Charon. As for the → Earth-Moon system, billions of years from now, the Earth and the Moon will have the same period of rotation, and these will also exactly equal the orbital period of the Moon around the Earth. → tidal friction.
Fr.: rupture par effet de marée
The disruption of an extended astronomical object under the action of the → tidal forces exerted by another nearby object.
tidal disruption flare
âlâv-e gosixt-e kešandi
A luminosity enhancement in the → light curve of a galaxy observed in X-rays or ultraviolet surveys supposed to be associated with the → tidal disruption of a star that has passed close to a → supermassive black hole in the core of a → host galaxy. An → accretion disk forms after the tidal disruption. The flare event marks the beginning of the accretion process onto the black hole.
joft-e Tusi (#)
Fr.: couple de Tusi
Named for Nasireddin Tusi (1201-1274), director of Marâgha observatory who created the Ilkhani zij; → couple.
Type I supernova
abar-now-axtar-e gune-ye I
Fr.: supernova de type I
A type of supernova whose spectra lacks hydrogen lines. Its → light curve exhibits a sharp maximum with a gradual decrease. Typical magnitudes MV = -14 to -17. Ejecta velocities about 10,000 km/sec. Type I supernovae have several subtypes: → Type Ia, → Type Ib, and → Type Ic.
Type Ia supernova
abar-now-axtar-e gune-ye Ia
Fr.: supernova de type Ia
A → Type I supernova that presents a singly-ionized silicon (Si II) absorption feature at 6150 Å near peak brightness. Type Ia SNe are believed to result from mass → accretion to a carbon-oxygen → white dwarf in a → close binary system. When the white dwarf mass exceeds the → Chandrasekhar limit, the → degenerate electron pressure can no longer support the accumulated mass and the star collapses in a thermonuclear explosion producing a supernova. The → peak luminosity of SNe Ia is set by the radioactive decay chain 56Ni → 56Co → 56Fe, and the observed photometric correlation between the peak luminosity and the time-scale over which the → light curve decays from its maximum is understood physically as having both the luminosity and → opacity being set by the mass of 56Ni synthesized in the explosion. Type Ia supernovae occur in all types of galaxies. Type Ia SNe are used as → standard candles in determining cosmological distances, after normalizing their light curves with the → Phillips relation.
Type Ib supernova
abar-now-axtar-e gune-ye Ib
Fr.: supernova de type Ia
A → Type I supernova that has neutral helium line (He I) at 5876 Å, and no strong silicon (Si II) absorption feature at 6150 Å. Type Ib supernovae are believed to result from the evolution of → massive stars.
Type Ic supernova
abar-now-axtar-e gune-ye Ic
Fr.: supernova de type Ia
Type II supernova
abar-now-axtar-e gune-ye II
Fr.: supernova de type II
A supernova type whose spectrum contains hydrogen lines. Compared with → Type I supernovae, its → light curve has a broader peak at maximum and dies away more rapidly. The magnitudes are smaller, ranging from MV = -12 to -13.5, and the ejecta have lower velocities (about 5,000 km/sec). These supernovae, which result from the final evolution of → massive stars, have three main divisions: → Type II-P, → Type II-L, and → Type II-n.
Type II-L supernova (SN II-L)
abar-now-axtar-e gune-ye II-L
Fr.: supernova de type II-L
Type II-n supernova (SN II-n)
abar-now-axtar-e gune-ye II-n
Fr.: supernova de type II-n