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rotational mixing âmizeš-e carxeši Fr.: mélange rotationnel A consequence of → stellar rotation that deforms the star, triggers instabilities (→ shear turbulence and → meridional currents) leading to → transport of chemical species in the star. The efficiency of rotational mixing (measured for instance by the degree of surface → enrichments at a given → evolutionary stage) increases when the initial mass and rotation increase. This efficiency increases also when the initial → metallicity decreases. This is due to the fact that when the metallicity is lower, the stars are more compact. This makes the → gradients of the → angular velocity steeper in the stellar interiors. Steeper gradients produce stronger shear turbulence and thus more mixing. Rotational mixing can bring to the surface heavy elements newly synthesized in the stellar core. Rotation thus produces an increase of the → opacity of the outer layers and activates strong → mass loss through → radiatively driven winds. This effect may be responsible for the loss of large fractions of the initial mass of the star (Meynet et al. 2007, arXiv:0709.2275). → rotational; → mixing. |
rotational modulation (ROT) degarâhangeš-e carxeši Fr.: modulation rotationnelle A very small variation in the surface brightness of a single star due to its rotation. Several types of stars are known to have photospheric spots. Brightness variation occurs as rotation carries star spots or other localized activity across the line of sight. → rotational; → modulation. |
rotational motion jonbeš-e charkheshi Fr.: mouvement de rotation Of a → rigid body, a motion in which there are always two points of the body which remain motionless. → rotational; → motion. |
rotational period dowre-ye carxeš Fr.: période de rotation → rotational; → period. |
rotational transition gozareš-e carxeši Fr.: transition rotationnelle A slight change in the energy level of a molecule due to the rotation of its constituent atoms about their center of mass. → rotational; → transition. |
rotational velocity tondâ-ye catxeši Fr.: vitesse de rotation The velocity of a → rotational motion; same as → angular velocity. → rotational; → velocity. |
Roxburgh criterion sanjidâr-e Roxburgh Fr.: critère de Roxburgh An integral constraint used to quantify the uncertainty on the extent of → convective overshooting and its effect on models of stars. Roxburgh, I. 1989, A&A, 211, 361; → criterion. |
rule of decision razan-e vâsun Fr.: régle de décision Same as → significance testing and → test of significance. |
Rydberg correction aršâyeš-e Rydberg Fr.: correction de Rydberg A term inserted into a formula for the energy of a single electron in the outermost shell of an atom to take into account the failure of the inner electron shells to screen the nuclear charge completely. → rydberg; → correction. |
Saha equation hamugeš-e Saha Fr.: équation de Saha An equation that gives the number of atoms of a given species in various stages of → ionization that exist in a gas in → thermal equilibrium as a function of the temperature, density, and ionization energies of the atoms. Named after the Indian astrophysicist Megh Nad Saha (1894-1956), who first derived the equation in 1920; → equation. |
Saiph (κ Orionis) Seyf (#) Fr.: Saiph A → supergiant star of visual magnitude 2.06 and → spectral type B0.5 Ia marking the right knee of Orion. It is about 700 light-years away. Saiph "sword," from Ar. as-saiph al-jabbâr
( |
Sakharov conditions butârhâ-ye Sakharov Fr.: conditions de Sakharov The three conditions that are necessary for the generation of a
→ baryon asymmetry in the
→ early Universe. These conditions are: Named after Andrei Sakharov (1921-1989), who in 1967 described these three minimum conditions (A. D. Sakharov, 1967, Zh. Eksp. Teor. Fiz. Pis'ma 5, 32; 1967, JETP Lett. 91B, 24); → condition. |
Salpeter function karyâ-ye Salpeter Fr.: équation de Salpeter The first mathematical description of the → initial mass function (IMF) of newly formed stars of solar to → intermediate-masses. It is proportional to M^{ -2.35}, where M is the stellar mass. → Salpeter slope. Named after the Austrian-Australian-American astrophysicist Edwin Ernest Salpeter (1924-2008); → function. |
saturated solution luyeš-e anjâlidé Fr.: solution saturée A solution which can exist in equilibrium with excess of solute. The saturation concentration is a function of the temperature. |
saturation anjâl, anjâleš Fr.: saturation Physics: Degree of magnetization of a substance which cannot be exceeded
however strong the applied magnetizing field. Verbal noun of → saturate. |
saturation current jarayân-e anjâl, ~ anjâleš Fr.: courant de saturation The maximum current that can be obtained in a specific circuit under specified conditions. → saturation; → current. |
saturation induction darhâzeš-e anjâl, ~ anjâleš Fr.: induction à saturation The maximum intrinsic magnetic induction possible in a material. → saturation; → induction. |
saturation signal nešâl-e anjâl, ~ anjaalesh Fr.: signal de saturation, ~ saturé In radar, a signal whose amplitude is greater than the dynamic range of the receiving system. → saturation; → signal. |
scalar perturbation partureš-e marpeli Fr.: perturbation scalaire The energy density fluctuations in the → photon-baryon plasma that bring about hotter and colder regions. This perturbation creates velocity distributions that are out of phase with the acoustic density mode. The fluid velocity from hot to cold regions causes blueshift of the photons, resulting in → quadrupole anisotropy. → scalar; → perturbation. |
Schechter function karyâ-ye Schechter Fr.: fonction de Schechter A mathematical expression that describes the → luminosity function of galaxies. The function correctly reflects the facts that the luminosity function decreases with increasing luminosity and that the decrease is particularly marked at high luminosities. It is expressed as: φ(L) = φ^{*}(L/L^{*})^{α} exp (-L/L^{*}), which has two parts and three parameters: φ^{*} is an empirically determined amplitude, α is an empirically derived exponent, and L^{*} is a characteristic luminosity which separates the low and high luminosity parts. For small luminosities (L much smaller than L^{*}) the Schechter function approaches a power law, while at high luminosities (L much larger than L^{*}) the frequency of galaxies drops exponentially. φ^{*}, L^{*}, and the faint-end slope α depend on the observed wavelength range, on the → redshift, and on the environment where the galaxies are observed. Named after the American astronomer Paul Schechter (1948-), who proposed the function in 1976 (ApJ 203, 297); → function. |
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