Each photometric value is an average over the visible surface. Thus complex light curves such as those of 25 Sex imply that over the photosphere there are regions with somewhat different energy distributions. With differences in the stellar opacities due both to abundance and magnetic field differences, the line blanketing and flux redistribution from the ultraviolet change from one location on the surface to another. These need to be modeled with the help of magnetic and spectral data. The photometry is both a constraint and an initial step in this process.
Acknowledgements
This work was supported in part by NSF grant AST-9115114 to The Citadel and in part by grants from The Citadel Development Foundation. I appreciate the continuing efforts of Louis J. Boyd and Robert J. Dukes Jr., to keep the FCAPT operating properly.