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Optical depth and actual depth, and respectively, can vary widely depending on the absorptivity of the astrophysical environment. Indeed, τ {\displaystyle \tau } is able to show the relationship between these two quantities and can lead to a greater understanding of the structure inside a star .
Spectral optical depth or spectral optical thickness is the natural logarithm of the ratio of incident to transmitted spectral radiant power through a material. [1] Optical depth is dimensionless , and in particular is not a length, though it is a monotonically increasing function of optical path length , and approaches zero as the path length ...
A-type star In the Harvard spectral classification system, a class of main-sequence star having spectra dominated by Balmer absorption lines of hydrogen. Stars of spectral class A are typically blue-white or white in color, measure between 1.4 and 2.1 times the mass of the Sun, and have surface temperatures of 7,600–10,000 kelvin.
ICRF – (astrophysics terminology) International Celestial Reference Frame, a coordinate system based on radio sources used to define the locations of objects in the sky; ICRS – (astrophysics terminology) International Celestial Reference System, a coordinate system based on Hipparcos observations used to define the locations of objects in ...
The Planck collaboration version of the ΛCDM model is based on six parameters: baryon density parameter; dark matter density parameter; scalar spectral index; two parameters related to curvature fluctuation amplitude; and the probability that photons from the early universe will be scattered once on route (called reionization optical depth). [18]
The grey atmosphere (or gray) is a useful set of approximations made for radiative transfer applications in studies of stellar atmospheres (atmospheres of stars) based on the simplified notion that the absorption coefficient of matter within a star's atmosphere is constant—that is, unchanging—for all frequencies of the star's incident radiation.
Subscripts 1 and 2 refer to initial and final optical media respectively. These ratios are sometimes also used, following simply from other definitions of refractive index, wave phase velocity, and the luminal speed equation:
For the water masers, the inner and outer radii limits roughly correspond to the density limits for maser operation. At the inner boundary, the collisions between molecules are enough to remove a population inversion. At the outer boundary, the density and optical depth is low enough that the gain of the maser is diminished.