iron opacity peak
setiq-e kederi-ye âhan
Fr.: pic d'opacité du fer
A bump appearing in the plot of stellar → opacity versus temperature. The ionization of the heaviest → chemical elements, especially → iron, which is the most abundant heavy metal, produces a large number of weak spectral → absorption lines. These lines dominate the stellar opacity in the temperature range 105-106 K and furnish two local opacity peaks: a large peak around 2 × 105 K and a smaller one around 1.5 × 106 K (Rogers & Iglesias, 1992, ApJS 79, 507; Iglesias et al. 1992, ApJ, 397, 717).
Kramers' opacity law
qânun-e kederi-ye Kramers (#)
Fr.: loi de l'opacité de Kramers
Same as → Kramers' law.
Named after Henrik Kramers (1894-1952); → law.
Fr.: opacité monochromatique
The sum of → absorption coefficient (κν) and → scattering coefficient (σν) at a given frequency: kν = κν + σν. See also the → Rosseland mean opacity.
→ monochromatic; → opacity.
1) General: The state or quality of being opaque.
From Fr. opacité, from L. opacitatem (nom. opacitas) "shade, shadiness," from opacus "shaded, dark, opaque."
Kederi, from keder "opaque," from Ar. kader + -i suffix forming nouns from adjectives.
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).
Named after Svein Rosseland (1894-1985), a Norwegian astrophysicist, who obtained the expression in 1924; → mean; → opacity.