Balmer limit hadd-e Bâlmer Fr.: limite de Balmer The wavelength in the blue end of the → Balmer series, at 3646 Å, near which the separation between successive lines decreases and approaches a → continuum. |
canonical upper limit hadd-e zabarin-e jerm Fr.: limite supériure canonique A physical upper mass limit near 150 Msun assumed for the stellar → initial mass function (Kroupa et al. 2012, arXiv:1112.3340). |
central limit theorem farbin-e hadd-e markazi Fr.: théorème central limite A statement about the characteristics of the sampling distribution of means of → random samples from a given → statistical population. For any set of independent, identically distributed random variables, X_{1}, X_{2},..., X_{n}, with a → mean μ and → variance σ^{2}, the distribution of the means is equal to the mean of the population from which the samples were drawn. Moreover, if the original population has a → normal distribution, the sampling distribution of means will also be normal. If the original population is not normally distributed, the sampling distribution of means will increasingly approximate a normal distribution as sample size increases. |
Chandrasekhar limit hadd-e Chandrasekhar (#) Fr.: limite de Chandrasekhar A limiting mass of about 1.44 Solar masses that the theory predicts a non-rotating → white dwarf can attain without collapsing to become a → neutron star or a → black hole. Over this → critical mass, the degeneracy pressure will be unable to bear the load of the bulk mass. Named after Subrahmayan Chandrasekhar (1910-1995), Indian-born American astrophysicist who, with William A. Fowler, won the 1983 Nobel Prize for Physics for his research on white dwarfs; → limit. |
confusion limit hadd-e pašeš Fr.: limite de confusion The → fluctuations of the → background → sky brightness below which astronomical → sources cannot be → detected individually. The confusion limit is reached when the density of sources brighter than the → root mean square → noise becomes high enough within the area of the resolution element. |
diffraction-limited karânmand bé parâš Fr.: limité par la diffraction The quality of an → optical system that is capable of producing images with angular resolution as small as the theoretical limit of the → Airy disk. → diffraction; limited, adj. of → limit. Karânmand "bounded, limited," from karân→ boundary + -mand possession suffix; parâš→ diffraction. |
Eddington limit hadd-e Eddington (#) Fr.: limite d'Eddington The theoretical upper limit of → luminosity at which the → radiation pressure of a light-emitting body would exceed the body's → gravitational attraction. A star emitting radiation at greater than the Eddington limit would break up. The Eddington luminosity for a non-rotating star is expressed as: L_{Edd} = 4πGMm_{p}cσ_{T}^{-1}, where G is the → gravitational constant, M the star mass, m_{p} the → proton mass, c the → speed of light, and σ_{T} the → Thomson cross section. It can also be written as L_{Edd} = 4πGMcκ^{-1}, where κ is the → opacity. In terms of solar mass, the Eddington limit can be expressed by: L_{Edd} = 1.26 × 10^{38} (M/Msun) erg s^{-1}. See also → rotational Eddington limit. Named after Arthur Stanley Eddington (1882-1944), prominent British astrophysicist; → limit. |
elastic limit hadd-e kešâyand Fr.: limite d'élasticité, ~ élastique The smallest → stress beyond which a → solid body can no longer return to its original shape. The material ceases to obey → Hooke's law. Also called → yield point. |
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. |
Humphreys-Davidson limit hadd-e Humphreys-Davidson Fr.: limite de Humphreys-Davidson An empirical upper → luminosity boundary in the → H-R diagram. It consists of two sections, a sloping part and a horizontal part. The sloping part, which decreases with decreasing → effective temperature, corresponds roughly to the → Eddington limit. The horizontal part is the temperature-independent upper luminosity limit for late-type → hypergiants. It is thought that → massive stars above the Humphreys-Davidson limit encounter an → instability, possibly due to the opacity-modified Eddington limit, and experience high → mass loss episodes which prevent their evolution to cooler temperatures. → Luminous Blue Variable stars are examples of this high mass loss phase. Named after Roberta M. Humphreys and Kris Davidson, who first dealt with this limit (1979, ApJ 232, 409); → limit. |
limit hadd (#) Fr.: limite 1) General: The final, utmost, or furthest → boundary or
→ point as to extent, amount, continuance, procedure, etc. From O.Fr. limite "a boundary," from L. limitem (nom. limes) "a boundary, embankment between fields, border," related to limen "threshold." Loan from Ar. Hadd "limit, term." |
limited haddmand Fr.: limité Confined within limits; restricted or circumscribed. Adj. of → limit. |
limiting magnitude borz-e hadd Fr.: magnitude limite The faintest magnitude reachable by an instrument. |
lunar ecliptic limit hadd-e hurpehi-ye mâh Fr.: limite écliptique de la Lune The farthest distance from a → lunar orbit node within which, if the Moon happens to be at full, a lunar eclipse may occur. The lunar ecliptic limit extends about 12° on each side of the node. |
Lyman limit hadd-e Lyman Fr.: limite de Lyman The short-wavelength end of the hydrogen Lyman series, at 912 Å. Also called → Lyman continuum. It corresponds to the energy (13.6 eV) required for an electron in the hydrogen ground state to jump completely out of the atom, leaving the atom ionized. |
magnitude-limited survey bardid bâ borz-e haddmand Fr.: relevé limité en magnitude A survey in which the observed objects are bighter than a given → apparent magnitude. |
Newtonian limit hadd-e Newtoni Fr.: limite newtonienne The limit attained by → general relativity when velocities are very smaller than the → speed of light or gravitational fields are weak. This limit corresponds to the transition between general relativity and the → Newtonian mechanics. See also → Newtonian approximation. |
Oort limit hadd-e Oort Fr.: limite de Oort 1) The upper limit for the density of all matter in the plane of the Galaxy near the Sun's
locality, as calculated from the velocities and distribution of stars
in relation to the gravitational field of the Galactic disk. The value is
0.14 solar masses per cubic parsec, or 9.5 x 10^{-24} g cm^{3}. → Oort cloud; → limit. |
Oppenheimer-Volkoff limit hadd-e Oppenheimer-Volkoff Fr.: limite d'Oppenheimer-Volkoff The upper bound to the mass of a → neutron star, the mass beyond which the pressure of neutron → degenerate matter is not capable of preventing the → gravitational collapse which will lead to the formation of a → black hole. Modern estimates range from approximately 1.5 to 3.0 → solar masses. The uncertainty in the value reflects the fact that the → equation of state for → overdense matter is not well-known. Oppenheimer, J.R., Volkoff, G.M., 1939, Physical Review 55, 374. Named after Robert Oppenheimer (1904-1967), an American theoretical physicist, and George Volkoff (1914-2000), a Canadian physicist, who first calculated this limit. Oppenheimer is widely known for his role as the scientific director of the Manhattan Project, the World War II effort to develop the first nuclear weapons at the secret Los Alamos laboratory in New Mexico; → limit. |
photon tiring limit hadd-e xastegi-ye foton Fr.: limite par fatigue du photon The maximum → mass loss rate of a star when the → wind luminosity equals the total available → stellar luminosity. The mechanical luminosity of the wind at infinity is given by: L_{wind} = Mdot (v_{∞}^{2}/2 + GM/R) = Mdot (v_{∞}^{2}/2 + v_{esc}^{2}/2). For L_{wind} = L_{*}, the mass loss rate is Mdot_{max} = 2L_{*}/(v_{∞}^{2} + v_{esc}^{2}). Following Owoki & Gayly (1997), Mdot_{tir} is the maximum mass loss rate when the wind just escapes the gravitational potential, with v_{∞} tending toward zero. Mdot_{tir} is much larger than typical mass loss rates from → line-driven winds, where the driving lines become saturated with increasing density limiting the wind mass loss rates to about 10^{-4} Msun yr^{-1} in even the most luminous stars. → photon; tiring, from tire "to weary; become weary," → tired; → limit. |