Diagnostic diagrams used to characterize the stellar parameters of the stripped star, and its contribution to the total flux. Left-hand panel: fit diagram showing reduced-χ² contours defining the best fitting and silicon abundance. Right-hand panel: dependence of best fitting silicon abundance on percentage contribution of the Bstr star to the V-band, and as a function of helium abundance. The horizontal dotted line indicates solar abundance, and the vertical line is the 55% contribution adopted by Shenar et al. (2020).