pulsâr-e dotâyi, tapâr-e ~ (#)
Fr.: pulsar double
A → binary pulsar consisting of two pulsars. The only known example is PSR J0737-3039 (A and B), discovered in 2003 (Burgay et al. Nature 426, 531). The rotation periods of the pulsars are 22.7 and 2.8 milliseconds respectively. Each of them has a mass about 1.3 times that of the Sun and revolves around their → center of gravity with a period of 2.4 hours. According to the theory of → general relativity, such a binary should lose energy through the emission of → gravitational waves. As deduced from the change in orbital period, the separation of the pulsars is reducing by about 7 mm per day, in exact agreement with theory. It is expected that the pulsars will eventually merge in about 85 million years.
Fr.: double réfraction
Formation of two refracted rays of light from a single incident ray; property of certain crystals, notably calcite.
Fr.: racine double
double shell burning
suzeš-e puste-ye dotâyi
Fr.: combustion double coquille
A situation in the evolution of an → asymptotic giant branch star whereby both hydrogen and helium shells provide energy alternatively. As the burning → helium shell approaches the hydrogen-helium discontinuity, its luminosity decreases because it runs out of the fuel. As a consequence, the layers above contract in response, thus heating the extinguished → hydrogen shell until it is re-ignited. However, the shells do not burn at the same rate: the He burning shell becomes thermally unstable and undergoes periodic → thermal pulses.
šekâf-e dotâyi (#)
Fr.: fente double
A pair of adjacent holes or slits made on a dark and plane surface, used in optical experiments, such as interference and diffraction.
setâre-ye dotâyi (#)
Fr.: étoile double
An apparently single star which better observational resolution shows it to be a pair of closely lying stars. They may or may not be physically related.
Fr.: vision double
Same as → diplopia.
double white dwarf
sefid kutule-ye dotâyi
Fr.: naine blanche double
A → double-lined binary with two → white dwarf components. Short-period double white dwarfs can lose → orbital angular momentum by emitting → gravitational radiation and if the total mass of the binary exceeds the → Chandrasekhar limit, their eventual → merger might produce a → Type Ia supernova.
double-degenerate binary system
râžmân-e dorin-e dobâr vâgen
Fr.: système binaire doublement dégénéré
A system of evolved → binary stars in which both → components have ejected their envelopes and evolve toward → white dwarf stage. So far a half dozen double-degenerate → binary systems are known, for example Henize 2-248 (M. Santander-Garcia et al., 2015, 518, 5).
hambaz-e do paxši
An instability involving two layers of fluid with opposite gradients of properties. Same as → fingering instability. See also → salt finger. Double-diffusive instabilities commonly occur in any astrophysical fluid that is stable according to the → Ledoux criterion, as long as the entropy and chemical stratifications have opposing contributions to the dynamical stability of the system. They drive weak forms of convection, and can cause substantial heat and compositional → mixing. Two cases can be distinguished. In fingering convection, entropy is stably stratified (∇ - ∇ad < 0), but chemical composition is unstably stratified (∇μ < 0); it is often referred to as → thermohaline convection by analogy with the oceanographic context in which the instability was first discovered. In oscillatory double-diffusive convection, entropy is unstably stratified (∇ - ∇ad > 0), but chemical composition is stably stratified (∇μ > 0); it is related to semiconvection, but can occur even when the → opacity is independent of composition (P. Garaud, 2014, arXiv:1401.0928).
Fr.: binaire à double raies
double-lined eclipsing binary
dorin-e gerefti-ye doxatté
Fr.: binaire à éclipse à double raies
double-lobed radio source
xan-e râdioyi bâ lap-e dotâyi
Fr.: radio source à double lobe
A → galaxy that emits radio energy from two regions located on opposite sides of the galaxy.
âzmâyeš-e šekâf-e dotâyi (#)
Fr.: expérience de double fente
A pair of forbidden spectral lines of the same atom arising from
a common upper excitation level, for example [O III] λ 5007 and
[O III] λ 4959, [N II] λ 6584 and [N II] λ 6548, and [S II] λ 6717,
[S II] λ 6731.
From O.Fr. doublet, from → double + -et diminutive suffix.
Dotâyé, from dotâ→ double + -(y)é nuance suffix.
dobâr-, dv-, dotâyi
Fr.: double, à ~
dobâr yonidé (#)
Fr.: deux fois ionisé
An atom that has lost two of its external electrons, for example O++ ([O III]).
doubly refracting crystal
bolur-e šakst-e dotâyi
Fr.: cristal à double réfraction
A → transparent → crystalline substance (such as calcite, quartz, and tourmaline) that is → anisotropic relative to the → speed of light. A ray incident normally on such crystals is broken up into two rays in traversing the crystal, → ordinary ray and → extraordinary ray.
Fr.: en bas, vers le bas
M.E. doun, from O.E. dune "downward," short for adune, ofdune, from a-, of "off, from" + dune "hill."
Pâyin "bottom, below; at the foot of," from pâ(y) "foot; step;" Mid.Pers. pâd, pây; Av. pad- "foot;" cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-.