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 = 4πMR2/5T.
Fr.: axe de rotation
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 ve. sini, where ve 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 Eddington limit
hadd-e Eddington-e carxeši
Fr.: limite d'Eddington avec rotation
The → Eddington limit of luminosity for a → rotating star in which both the effects of → radiative acceleration and rotation are important. Such objects mainly include → OB stars, → LBV, → supergiants, and → Wolf-Rayet stars. It turns out that the maximum permitted luminosity of a star is reduced by rotation, with respect to the usual Eddington limit (Maeder & Meynet, 2000, A&A, 361, 159).
Fr.: énergie rotationnelle
The → kinetic energy due to the → rotation of and object. Rotational energy is part of the total kinetic energy of the body. It is given by: (1/2)Iω2, where I is the → moment of inertia and ω is the → angular velocity. Same as → angular kinetic energy.
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 modulation (ROT)
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.
Fr.: mouvement de rotation
Of a → rigid body, a motion in which there are always two points of the body which remain motionless.
Fr.: période de rotation
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.
Fr.: vitesse de rotation
carxandé (#), carxânandé (#)
A device that rotates or causes rotation.
Agent noun from → rotate.
A rotating part of an electrical apparatus, e.g. the armature of a generator,
or of a mechanical device.
Carxâ agent noun of carxidan, → rotate.
Fr.: ligne, rangée
CCD detector: Series of pixels arranged along a line. → column
O.E. ræw "a row, line;" cf. Du. rij "row;" O.H.G. rihan "to thread," riga "line;" Ger. Reihe "row, line, series."
Raj "line, row," variants raž, rak, râk, rezg (Lori), ris, risé, radé, rasté, râsté, related to râst "right, true; just, upright, straight;" Mid.Pers. râst "true, straight, direct;" Soghdian rəšt "right;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" cf. Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" PIE base *reg- "move in a straight line," hence, "to direct, rule."
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.
RR Lyrae star
setâre-ye RR Cang
Fr.: étoile RR Lyrae
A member of a large class of → pulsating stars of type A2-F6 with periods less than 1 day. They are similar to → Cepheids, except that their periods are much shorter and are less luminous. RR Lyrae stars belong to → Population II and are often found in → globular clusters (hence one of their older names cluster variables) or elsewhere in the → galactic halo. They are used as distance indicators (→ standard candle) out to more than 200 kpc.
A metallic chemical element; symbol Rb. Atomic number 37; atomic weight 85.4678; melting point 38.89°C; boiling point 686°C; specific gravity 1.53 at 20°C. It was discovered in the mineral lepidolite by the German chemist Robert Wilhelm Bunsen and the German physicist Gustav-Robert Kirchoff in 1861. Bunsen isolated rubidium in 1863.
From L. rubidus "deep red," because of the two "deep red lines" in its spectra.
yâqut (#), yâkand (#)
Red form of corundum, Al2O3, which owes its color to traces of chromium. Used in laser as a gem stone.
M.E. rubi, from O.Fr. rubi, from M.L. rubinus lapis "red stone," from L. rubeus "red," related to ruber→ red.
Yâqut, yâkand related to Gk. hyakinthos "hyacinth," probably ult. from a non-I.E. Mediterranean language.
Fr.: Tables rudolphines
A set of astronomical tables created in 1627 by Johannes Kepler (1571-1630) based on observations by Tycho Brahe (1546-1601). These tables allowed Kepler to derive the three laws of planetary motions bearing his name (→ Kelpler's laws). These are the first tables in which → atmospheric refraction has been taken into account. They overruled the → Prutenic Tables.
From the L. title Tabulae Rudolphinae, in memory of Rudolf II (1552-1612), king of Hungary and Bohemia, and Holy Roman Emperor; → table.
Fr.: méthode de Ruffini-Horner
A method for finding the value of a → polynomial given by a real number and deriving its → roots. It consists essentially of factoring the polynomial in a nested form. Also known as → nested multiplication.
Named after Paolo Ruffini (1765-1822) and William Horner (1786-1837), who independently elaborated the method; → method.