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Rosseland mean opacity kederi-ye miyângin-e Rosseland Fr.: opacité moyenne de Rosseland The → opacity of a gas of given composition, temperature, and density averaged over the various wavelengths of the radiation being absorbed and scattered. The radiation is assumed to be in → thermal equilibrium with the gas, and hence have a → blackbody spectrum. Since → monochromatic opacity in stellar plasma has a complex frequency dependence, the Rosseland mean opacity facilitates the analysis. Denoted κ_{R}, it is defined by: 1/κ_{R} = (π/4σT^{3}) ∫(1/k_{ν}) (∂B/∂T)_{ν}dν, summed from 0 to ∞, where σ is the → Stefan-Boltzmann constant, T temperature, B(T,ν) the → Planck function, and k_{ν} monochromatic opacity (See Rogers, F.J., Iglesias, C. A. Radiative atomic Rosseland mean opacity tables, 1992, ApJS 79, 507). Named after Svein Rosseland (1894-1985), a Norwegian astrophysicist, who obtained the expression in 1924; → mean; → opacity. |
Rossiter-McLaughlin effect oskar-e Rossiter-McLaughlin Fr.: effet Rossiter-McLaughlin A → spectroscopic phenomenon observed when either an → eclipsing binary's → secondary star or an → extrasolar planet is seen to → transit across the face of the → primary body. Because of the rotation of the star, an asymmetric distortion takes place in the → line profiles of the stellar spectrum, which changes during the transit. The measurement of this effect can be used to derive the → alignment of the → orbit of the transiting exoplanet with respect to the → rotation axis of the star. Named after Richard Alfred Rossiter (1886-1977) and Dean Benjamin McLaughlin (1901-1965), American astronomers. |
rotate carxidan (#) Fr.: tourner To turn around an axis. See also → revolve. From L. rotare "to cause to spin, roll, move in a circle," from L. rota "wheel;" cognate with Pers. râh "way, path" (from Mid.Pers. râh, râs "way, street," also rah, ras "chariot;" from Proto-Iranian *rāθa-; cf. Av. raθa- "chariot;" Skt. rátha- "car, chariot," rathyā- "road;" Lith. ratas "wheel;" O.H.G. rad; Ger. Rad; Du. rad; O.Ir. roth; PIE *roto- "to run, to turn, to roll"). Carxidan "to rotate," from carx "every thing performing a circulatory motion; a wheel; a cart;" Mid.Pers. chr "wheel," Parthian cxr "wheel;" Ossetic calx "wheel;" Av. caxra- "wheel;" cognate with Skt. cakra- "wheel, circle; cycle," carati "he moves, wanders;" Gk. kyklos "circle, wheel," polos "axis of a sphere," polein "move around;" L. colere "to dwell in, to cultivate, move around," colonus "farmer, settler;" O.E. hweol "wheel;" Rus. koleso "wheel." |
rotating carxandé, carxân Fr.: en rotation Capable of or having rotation. |
rotating black hole siyahcâl-e carxân Fr.: trou noir en rotation A black hole that possesses angular momentum, as first postulated by Roy C. Kerr in 1963. Opposite of a stationary black hole. → ergosphere. → rotating; → black hole. |
rotating star setâre-ye carxân, ~ carxandé Fr.: étoile en rotation A star that has a non-zero → angular velocity. In a rotating star, the → centrifugal forces reduce the → effective gravity according to the latitude and also introduce deviations from sphericity. In a rotating star, the equations of stellar structure need to be modified. The usual spherical coordinates must be replaced by new coordinates characterizing the → equipotentials. See also → von Zeipel theorem. |
rotation carxeš (#) Fr.: rotation The motion of a body about its axis. Verbal noun of → rotate. |
rotation axis âse-ye carxeš Fr.: axe de rotation The imaginary line around which an object rotates. Same as → rotational axis and → axis of rotation. |
rotation curve xam-e carxeš Fr.: courbe de rotation A plot of the variation in → orbital velocity of stars and → interstellar matter with distance from the center of a → galaxy. A "flat" rotation curve indicates that the mass of the galaxy increases linearly with distance from its center. See also: farsi→ Keplerian rotation curve Rotation; → curve. |
rotation energy kâruž-e carxeš Fr.: énergie de rotation The → kinetic energy of rotational motion of an object. It is expressed by E_{R} = (1/2)Iω^{2}, where I is the → moment of inertia and ω → angular velocity (2π/P). |
rotation frequency basâmad-e carxeš Fr.: fréquence de rotation 1) The number of rotations per unit time of a rotating object. |
rotation period dowre-ye carxeš (#) Fr.: période de rotation The interval of time during which an object turns once about its axis. |
rotation phase fâz-e carxeš Fr.: phase de rotation A position parameter used in → stellar magnetic field studies. Its zero value represents the moment when, during → stellar rotation, the positive → magnetic pole is nearest to the → line of sight. |
rotation-induced turbulence âšubnâki-ye zâyide-ye carxeš, darhâzidé az ~ Fr.: turbulence induite par turbulence A type of → turbulence with motions more vigorous in the horizontal than in the vertical direction occurring in internal radiation zone of → rotating stars. Same as → shear turbulence. → rotation; → induced; → turbulence. |
rotation-powered pulsar (RPP) tapâr-e carxeš-tavân, pulsâr-e ~ ~ Fr.: A → neutron star that is spinning down as a result of → torques from → magnetic dipole radiation and particle emission. RPPs derive their energy primarily from the → rotation of the neutron star. The energy from their → spin-down appears as broad-band pulsations from → radio to → gamma-ray wavelengths and as a → wind of energetic particles flowing into their surrounding → pulsar wind nebulae. Since the discovery of RPPs through their radio → pulsations in 1967, more than 2000 → radio pulsars are now known with periods ranging from a few milliseconds to several seconds (A. K. Harding, 2013, Front. Phys. 8, 679). |
rotation-vibration spectrum binâb-e carxeš-šiveš Fr.: spectre rotation-vibration The spectrum of a molecule resulting from the simultaneous rotation and vibration of its constituent atoms. |
rotational carxeši (#) Fr.: rotationnel Of or pertaining to → rotation. |
rotational angular momentum jonbâk-e zâviyeyi-ye carxeši Fr.: moment angulaire rotationnel, moment cinétique ~ The → angular momentum of a body rotating about an axis. The rotational angular momentum of a solid homogeneous sphere of mass M and radius R rotating about an axis passing through its center with a period of T is given by: L = 4πMR^{2}/5T. → rotational; → angular; → momentum. |
rotational axis âse-ye carxeš Fr.: axe de rotation An imaginary line about which a solid object rotates. Same as → rotation axis and → axis of rotation. → rotational; → axis. |
rotational broadening pahneš-e carxeši Fr.: élargissement rotationnel The spectral line broadening caused by stellar rotation. Light from two rims of the star will be Doppler shifted in opposite directions, resulting in a line broadening effect. The line broadening depends on the inclination of the star's pole to the line of sight. The derived value is a function of v_{e}. sini, where v_{e} is the rotational velocity at the equator and i is the inclination, which is not always known. The fractional width (Δλ/λ) is of the order of 10^{-3} for B stars. → rotational; → broadening. |
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