Distribution of polarization and intensity of radiation across the stellar disk and numerical values of atmospheric characteristics governing this distribution

Details Distribution of polarization and intensity of radiation across the stellar disk and numerical values of atmospheric characteristics governing this distribution Distribution of polarization and intensity of radiation across the stellar disk and numerical values of atmospheric characteristics governing this distribution

Jan 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985ap%26ss.108...15b&link_type=abstract

Astrophysics and Space Science (ISSN 0004-640X), vol. 108, no. 1, Jan. 1985, p. 15-29.

Statistics

Computation

18

Atmospheric Scattering, Computational Astrophysics, Polarized Radiation, Radiation Distribution, Stellar Atmospheres, Stellar Radiation, Albedo, Atmospheric Models, Stellar Temperature, Supergiant Stars

Scientific paper

Computations of polarization and intensity of radiation from a unit stellar surface area are presented, as well as a study of the numerical characteristics of atmospheres - single-scattering albedo c»=,~ and the initial source function B~(~), which define the polarization behaviour of atmospheres. The radiatively stable models of stellar atmospheres presented by Kurucz et a!. (1974) and Kurucz (1979) have been used for calculations. Since the Q,~ ver'sus optical depth `r2 dependence is rather weak, it has been assumed that = const. With a fixed effective temperature Teff maximum values of Q are characteristic of stars featuring the lowest surface gravity acceleration g. Among stars with radiatively stable atmospheres, maximum values of Q = 5000 A) 0.4-0.6 are exhibited by supergiants with Teff = 8000-20000 K. The plot of Q(~) is characterized by discontinuities at the boundaries of spectral series for hydrogen and, sometimes, for helium. Maximum c»=2 are attained in the Lyman region of ~ = 912-1200 A, where Q~ can reach the value 0.7-0.9 for supergiants, this value being ~ 0.3 for Main-Sequence stars. For stars with TCff ~ 35000 K, high values of Q,~ also are attained for ~ < 912 A. Within the infrared region, c»=A is always small because of bremsstrahlung absorption. A rapid growth of the source function B2 with ~, typica' for ultraviolet range (within the Wien part of spectrum), together with high values of Q~ results in the strong polarization of emission from a unit stellar surface element, sometimes exceeding the values for the case of a pure electron scattering. For longer wavelengths, where the limb-darkening coefficient is smaller, the plane of polarization abruptly turns 90~ in the central parts of the visible stellar disk

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