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The large, faint H$\alpha$ emission surrounding the early B-star binary Spicahas been used to constrain the total hydrogen recombination rate of the nebulaand indirectly probe the Lyman continuum luminosity of the primary star. Earlyanalysis suggested that a stellar atmosphere model, consistent with Spica A'sspectral type, has a Lyman continuum luminosity about two times lower thanrequired to account for the measured H$\alpha$ surface brightness within thenebula. To more consistently model both the stellar and nebular emission, wehave used a model atmosphere for Spica A which includes the effects of gravitydarkening as input to photoionization models to produce synthetic H$\alpha$surface brightness distributions for comparison to data from the Southern$H\alpha$ Sky Survey Atlas (SHASSA).  This paper presents a method for the computation of projected surfacebrightness profiles from 1D volume emissivity models and constrains bothstellar and nebular parameters. A mean effective temperature for Spica A of$\simeq$ 24,800 K is sufficient to match both the observed absolutespectrophotometry, from the far-UV to the near-IR, and radial H$\alpha$ surfacebrightness distributions. Model hydrogen densities increase with the distancefrom the star, more steeply and linearly towards the southeast. The northwestmatter-bounded portion of the nebula is predicted to leak $\sim$17% of Lymancontinuum photons. Model H II region column densities are consistent witharchival observations along the line of sight.

Modeling the H$\alpha$ Emission Surrounding Spica using the Lyman Continuum from a Gravity-darkened Central Star