Analytical Reference Functions F(λ) for the Sun's Limb Darkening and Its Absolute Continuum Intensities (λλ 300 to 1100 m)

Author： Neckel Heinz

Publisher： Springer Publishing Company

ISSN： 0038-0938

Source： Solar Physics, Vol.229, Iss.1, 2005-06, pp. : 13-33

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Abstract

It is shown (1) that the coefficients A_i of the limb darkening functions i(μ)/i_center = P₅ (μ) = ∑A_i μⁱ (i = 0... 5; μ = cos θ), which had been published by Neckel and Labs (Solar Phys. 153, 91, 1994), can well be approximated by analytical functions of wavelength λ, and (2) that at first sight purely formal extrapolation of the functions P₅(μ) to the very limb (μ = 0.0) is not meaningless: in combination with absolute intensities for the disk center these functions yield ‘limb intensities’ which all correspond to almost the same ‘limb temperature’, T_limb≍4746 K. Together these results lead to ‘reference functions’ which can quickly yield rather reliable values of the Sun's continuum intensities, for any values of μ and λ.