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

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 Ω_λ and the initial source function_λ(δ_λ), which define the polarization behaviour of atmospheres. The radiatively stable models of stellar atmospheres presented by Kuruczet al. (1974) and Kurucz (1979) have been used for calculations. Since the Ω_λ versus optical depth τ_λ dependence is rather weak, it has been assumed that Ω_λ(τ_λ=cost. With a fixed effective temperatureT _eff maximum values of Ω are characteristic of stars featuring the lowest surface gravity accelerationg. Among stars with radiatively stable atmospheres, maximum values of Ω (λ=5000 Å) ≈ 0.4 0.6 are exhibited by supergiants withT _eff=8000 20 000 K. The plot of Ω(λ) is characterized by discontinuities at the boundaries of spectral series for hydrogen and, sometimes, for helium. Maximum Ω_λ are attained in the Lyman region of λ=912 1200 Å, where Ω_λ can reach the value 0.7 0.9 for supergiants, this value being ≳ 0.3 for Main-Sequence stars. For stars withT _eff ≳ 35 000 K, high values of Ω_λ also are attained for λ<912 Å. Within the infrared region, Ω_λ is always small because of bremsstrahlung absorption. A rapid growth of the source functionB _λ with <_λ typical for ultraviolet range (within the Wien part of spectrum), together with high values of Ω_λ 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.