Ratio between observed CoRoT flux, in instrumental units, and the flux predicted from model spectra vs. observed R magnitudes. The plotted points refer to a subsample of suitable and well characterized NGC 2264 members (see text), and symbols of different colors, largely overlapping with each other, refer to estimates obtained assuming four different values of log g between 3.0 and 4.5. The horizontal line refers to the adopted value, 4.2 × 10¹⁵ erg⁻¹ s⁻¹ cm⁻².