J Js'j where Gj (rs) gives the ratio of normal local to polar intensity due to gravity brightening:

where Tj and 7] denote the polar and local effective temperatures. The function aA(T) allowed the introduction of a model atmosphere into the Wilson-Devinney model. To elaborate, FGG(T) represents the monochromatic flux according to the Carbon-Gingerich model atmosphere (see Appendix E.1) tabulated in units of erg/cm2/s/ster/Hz in Carbon & Gingerich (1969). The implementation followed according to the definition aA(T) := Fcg(T)/Bv(x)(T). (6.3.9)

WD95, as a spin-off of the more recent version WD93K93 (see page 305), also includes the Kurucz stellar atmospheres models.

The WD model considers a simple reflection effect in a form close to that described in Sect. 3.2.5 and Appendix E.25, and, alternatively, a more detailed one which even considers multiple reflection developed by Wilson (1990), as described in Appendix E.25.

The present version of the WD program approximates the integral ( 3.2.49) by a simple sum but with fractional area corrections for eclipses, i.e., using (6.3.5) we get fn f2n cos Y 2

l($) =/ Xs ($) I (cos y; g, T ,A.)-- r2 sin 0 d<d0

where the sums are evaluated for angles < and 0 associated with visible points, denoting the grid size in < and 0. In the Wilson-Devinney program, the discretization is chosen as

7 In the Wilson-Devinney program (1993 and later versions), there is a flag LD which gives a choice among linear, logarithmic, and square-root limb-darkening laws. The effective limb-darkening factor Dj then changes and needs to be recomputed as outlined in Sect. 3.2.4. In all versions of the program, only x is an adjustable parameter, not y (Wilson 1998).

where N denotes the number of latitude circles on each hemisphere, and £ - 0.5

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