Baldwin-Phillips-Terlevich diagram nemudâr-e Baldwin-Phillips-Terlevich Fr.: diagram de Baldwin-Phillips-Terlevich A set of nebular → emission line diagrams used to distinguish the ionization mechanism of → nebular gas. The most famous version consists of [N II]λ6584/Hα versus [OIII] λ5007/Hβ. The next two more commonly used BPT diagnostics are [S II] λλ6717,6731/Hα versus [O III] λ5007/Hβ and [O I] λ6300/Hα versus [O III]λ5007/Hβ. These diagrams use strong, optical lines of close proximity in the ratios to limit → reddening and → spectrophotometric effects. They are able to clearly distinguish different classes of → ionization, for example → LINERs from normal → H II regions and → active galactic nuclei. Baldwin, J. A., Phillips, M. M., Terlevich, R., 1981 PASP 93, 5; → diagram. |
Becklin-Neugebauer object barâxt-e Becklin-Neugebauer Fr.: objet de Becklin-Neugebauer A compact infrared source in the Orion molecular cloud (OMC-1). It is thought to be a very dusty compact H II region surrounding a young B0 or B1 star. After Eric Becklin (1940-), and Gerry Neugebauer (1932-) who discovered the object in 1967; → object. |
Einstein-de Sitter effect oskar-e Einstein-de Sitter Fr.: effet Einstein-de Sitter Same as → geodetic precession. |
Einstein-de Sitter Universe giti-ye Einstein-de Sitter Fr.: Univers Einstein-de Sitter The → Friedmann-Lemaitre model of → expanding Universe that only contains matter and in which space is → Euclidean (Ω_{M} > 0, Ω_{R} = 0, Ω_{Λ} = 0, k = 0). The Universe will expand at a decreasing rate for ever. → Einstein; de Sitter, after the Dutch mathematician and physicist Willem de Sitter (1872-1934) who worked out the model in 1917; → Universe. |
Einstein-Hilbert action žireš-e Einstein-Hilbert Fr.: action de Einstein-Hilbert In → general relativity, the → action
that yields → Einstein's field equations.
It is expressed by: → Einstein; → Hilbert space; → action. |
Einstein-Podolsky-Rosen paradox pârâdaxš-e Einstein-Podolsky-Rosen Fr.: paradoxe Einstein-Podolsky-Rosen → EPR paradox. A. Einstein, B. Podolsky, N. Rosen: "Can quantum-mechanical description of physical reality be considered complete?" Phys. Rev. 41, 777 (15 May 1935); → paradox. |
Einstein-Rosen bridge pol-e Einstein-Rosen Fr.: pont d'Einstein-Rosen A hypothetical structure that can join two distant regions of → space-time through a tunnel-like shortcut, as predicted by → general relativity. The Einstein-Rosen bridge is based on the → Schwarzschild solution of → Einstein's field equations. It is the simplest type of → wormholes. Albert Einstein & Nathan Rosen (1935, Phys.Rev. 48, 73); → bridge. |
Greisen-Zatsepin-Kuzmin limit (GZK) hadd-e Greisen-Zatsepin-Kuzmin Fr.: limite de Greisen-Zatsepin-Kuzmin A theoretical limit of approximately 6 × 10^{19} → electron-volts for the energy of → cosmic rays above which they would lose energy in their interaction with the → cosmic microwave radiation background photons. Cosmic ray protons with these energies produce → pions on blackbody photons via the Δ resonance according to: γ_{CMB} + p → p + π^{0}, or γ_{CMB} + p → n + π^{+}, thereby losing a large fraction of their energy. These interactions would reduce the energy of the cosmic rays to below the GZK limit. Due to this phenomenon, → Ultra-high-energy cosmic rays are absorbed within about 50 Mpc. Named after Kenneth Greisen (1966), Physical Review Letters 16, 748 and Georgiy Zatsepin & Vadim Kuzmin (1966), Journal of Experimental and Theoretical Physics Letters 4, 78; → limit. |
in- 1) dar-; 2) nâ-, bi-, an-, a- Fr.: en- 1) Prefix meaning "into, in, on, upon, toward, at;" variants im-; il-; ir- by
assimilation of -n- with the following consonant. It occurs also sometimes
as en, in loans from O.Fr. 1) From L. in; cf. Gk. en; P.Gmc. *in (cf. O.Fris, Du., Ger.,
Goth. in); O.E. in, inne "within." 1) Dar- "in," from Mid.Pers. andar, → intra-. |
Kelvin-Helmholtz contraction terengeš-e Kelvin-Helmholtz Fr.: contraction de Kelvin-Helmholtz The contraction of a volume of gas under its → gravity, accompanied by the → radiation of the lost → potential energy as → heat. After the Scottish physicist William Thomson, also known as Lord Kelvin (1824-1907) and the German physicist and physician Hermann Ludwig Ferdinand von Helmholtz (1821-1894), who made important contributions to the thermodynamics of gaseous systems; → contraction. |
Kelvin-Helmholtz instability nâpâydâri-ye Kelvin-Helmholtz (#) Fr.: instabilité de Kelvin-Helmholtz An → instability raised when there is sufficient velocity difference across the interface between two uniformly moving → incompressible fluid layers, or when velocity → shear is present within a continuous fluid. |
Kelvin-Helmholtz mechanism sâzokâr-e Kelvin-Helmholtz Fr.: mécanisme Kelvin-Helmholtz The heating of a body that contracts under its own gravity. For a large body like a planet or star, gravity tries to compress the body. This compression heats the core of the body, which results in internal energy which in turn is radiated as → thermal energy. In this way a star could be heated by its own weight. William Thomson (Lord Kelvin) and Hermann von Helmholtz proposed that the sun derived its energy from the conversion of gravitational potential energy; → mechanism. |
Kelvin-Helmholtz time zamân-e Kelvin-Helmholtz Fr.: échelle de temps de Kelvin-Helmholtz The characteristic time that would be required for a contracting spherical cloud of gas to transform all its → gravitational energy into → thermal energy. It is given by the relation: t_{KH} ≅ GM^{2}/RL, where G is the → gravitational constant, M is the mass of the cloud, R the initial radius, and L the → luminosity. The Kelvin-Helmholtz time scale determines how quickly a pre-main sequence star contracts before → nuclear fusion starts. For the Sun it is 3 x 10^{7} years, which also represents the time scale on which the Sun would contract if its nuclear source were turned off. Moreover, this time scale indicates that the gravitational energy cannot account for the solar luminosity. For a → massive star of M = 30 Msun, the Kelvin-Helmholtz time is only about 3 x 10^{4} years. |
main-sequence fitting sazkard-e reshteh-ye farist Fr.: ajustement par la séquence principale The method of determining the distance to a star cluster by overlaying its main sequence on the theoretical zero-age main sequence and noting the difference between the cluster's apparent magnitude and the zero-age main sequence's absolute magnitude. → main sequence; → fitting. |
main-sequence turnoff rahgašt-e rešte-ye farist Fr.: tournant final de la séquence principale The point on the → Hertzsprung-Russell diagram of a star cluster at which stars begin to leave the → main sequence and move toward the → red giant branch. The main-sequence turnoff is a measure of age. In general, the older a star cluster, the fainter the main-sequence turnoff. Same as → turnoff point. → main sequence; → turnoff. |
spin-down kond-carxi Fr.: ralentissement A phenomenon in which the rotation period of a pulsar steadily decreases with the pulsar age. The cause of the spin-down is magnetic torque due to the strong fields threading out from the pulsar. The magnetic energy is being converted to high-energy particles and radiation from the nebula. Observed spin-down rates range from about 10^{-5} seconds/year for the youngest pulsars to about 10^{-12} seconds/year for recycled pulsars. The Crab pulsar is slowing down at a rate of about 10^{-5} seconds/year. Knowing the rotation period and the lengthening rate of a pulsar leads to its age. → spin; down, M.E.; O.E. ofdune "downward," from dune "from the hill." Kond-carxi, from kond "slow; dull" + carx→ rotate + -i noun suffix. |
spin-flip scattering parâkaneš bâ vâruni-ye espin Fr.: diffusion avec renversement du spin Quantum mechanics: The scattering of a particle that reverses the spin direction. → spin; flip, from flip-flap; → scattering. Parâkaneš, → scattering; bâ "with;" vâruni, noun from vârun, → inverse; espin, → spin. |
spin-orbit coupling jafsari-ye espin-madâr, jofteš-e ~ Fr.: couplage spin-orbite 1) Astro.: A relationship between the orbital period of one body around another
and its rotational period on its axis. The relationship results from tidal forces
between the two bodies. For example, the rotation period of the Moon equals its revolution
period around the Earth. |