2007A&A...470.1099C

The effects of irradiation on stellar limb darkening is still complicated to implement in light curve synthesis codes since it involves a large combination of parameters, including the effective temperatures of the source/irradiated stars, the apparent radius, and the angle of incidence of the infalling radiation field. This makes it too difficult to generalize how irradiation affects the limb darkening coefficients (LDCs). The aim of this paper is to present, in a suitable manner to be used directly in light curve synthesis codes, the effects of irradiation on the LDCs of convective atmospheres. To investigate the mutual irradiation of close binary systems, we have adopted a modified version of the UMA model atmosphere code with the upper boundary condition changed to take into account the external flux. Numerical improvements are also introduced, concerning the spatial resolution of the code (the number of µ points is increased from 6 to 18 points) and more modern models of atmospheres are adopted to simulate the hot companions. We have systematically studied the effects of irradiation on the LDCs of stellar atmospheres and present corrections to the LDCs to account for such effects. These corrections are given as a function of the relative flux for 12 commonly used passbands (Johnson-Cousins U B V R I J H K and Stroemgren u v b y) and can be easily implemented in light curve synthesis codes. A qualitative comparison with the few empirical measurements of LDCs indicates that the theoretical corrections give LDCs in better agreement with observations, particularly for interacting binary systems.