Testing Opacities Using the SED Variability of Chemically Peculiar Stars

Opacity variations across stellar surfaces are the key process producing the spectral energy distribution (SED) variability in chemically peculiar (CP) stars. The opacity variations are caused by the presence of surface spots with enhanced (or depleted) abundances of chemical elements. Simulations of the SED variability of chemically peculiar stars with abundances derived from Doppler mapping provide a detailed test of the continuum (bound free) and line opacities in the model atmospheres. The effect of opacities on the SED is most pronounced in the ultraviolet region. We simulate the ultraviolet and visual SED variability of selected chemically peculiar stars using model atmospheres calculated for actual surface abundances, and compare the predicted SEDs with observational results. We show that the simulations can reliably predict the observed SED and its variability as long as complete bound free and bound bound opacities are used. Therefore, the variability of chemically peculiar stars may serve as a test of opacities included in model atmospheres.