radial velocity method
raveš-e tondâ-ye šo'â'i
Fr.: méthode de vitesses radiales
The technique based on the analysis of the → radial velocity curve, used to detect the presence of an invisible secondary around a host star. This method holds the majority of exoplanet discoveries.
tondâ-ye dur šodan
Fr.: vitesse d'éloignement
The velocity with which an object moves away from another object or a reference point.
Fr.: théorème de réciprocité
1) General: Any theorem that expresses various reciprocal relations for the
behavior of some physical systems, in which input and output can be
interchanged without altering the response of the system to a given
Fr.: vitesse relative
For two objects A and B, the velocity which B, supposing itself at rest, assigns to A.
Fr.: vitesse relativiste
The velocity of a body when it is a significant fraction of the → speed of light.
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 κR, it is defined by: 1/κR = (π/4σT3) ∫(1/kν) (∂B/∂T)νdν, summed from 0 to ∞, where σ is the → Stefan-Boltzmann constant, T temperature, B(T,ν) the → Planck function, and kν monochromatic opacity (See Rogers, F.J., Iglesias, C. A. Radiative atomic Rosseland mean opacity tables, 1992, ApJS 79, 507).
Fr.: vitesse de rotation
The quality of the practices and theories that aim at establishing reproducible regularities in phenomena by using experimental method and providing a clearly formulated description.
Fr.: métallicité solaire
The proportion of the solar matter made up of → chemical elements heavier than → helium. It is denoted by Z, which represents the sum of all elements heavier than → helium, in mass fraction. The most recent determination of the solar Z gives a value of 0.0134 (Asplund et al. 2009, ARAA 47, 481), corresponding to the present-day photospheric composition.
tondâ-ye xoršid, ~ xoršidi
Fr.: vitesse solaire
The rate of change of the Sun's position with respect to the local standard of rest toward the → solar apex.
Fr.: vitesse spatiale
The velocity of a star relative to the Sun.
Fr.: métallicité stellaire
The metallicity derived from observations of stars in galaxies. It is mainly based on spectral → absorption lines in → ultraviolet (UV) and optical ranges. Stellar metallicity is a direct measure of the amount of metals in a galaxy, since large part of heavy elements lies in its stars.
Fr.: vitesse tangentielle
1) The instantaneous linear velocity of a body moving in a circular path.
It is equal to the → angular velocity multiplied
by the radius: vt = ωr.
Fr.: vitesse terminale
1) The constant maximum velocity reached by a body falling under gravity through a
liquid or gas, especially the atmosphere. The body ceases
to accelerate downward because the force of gravity is equal
to the opposing force of resistance by the medium.
The electricity produced by heat or temperature difference in a conductor.
Fr.: vitesse transverse
Same as → tangential velocity.
vector angular velocity
bordâr-e tondâ-ye zâviye-yi
Fr.: vecteur de vitesse angulaire
Of a rotating body, a vector of magnitude ω (→ angular velocity) pointing in the direction of advance of a right-hand screw which is turned in the direction of rotation.
The time rate of change of position in a given direction, measured as length per unit time. → speed.
L. velocitatem (nominative velocitas) "swiftness, speed," from velox (genitive velocis) "swift."
Tondâ, from tond "swift, rapid, brisk; fierce, severe" (Mid.Pers. tund "sharp, violent;" Sogdian tund "violent;" cf. Skt. tod- "to thrust, give a push," tudáti "he thrusts;" L. tundere "to thrust, to hit" (Fr. percer, E. pierce, ultimately from L. pertusus, from p.p. of pertundere "to thrust or bore through;" PIE base *(s)teud- "to thrust, to beat") + noun suffix -â.
Fr.: courbe de vitesse
A plot of the radial velocity of an object against time, derived from the Doppler shift of spectral lines.