Limb-darkening coefficients of illuminated atmospheres - I. Results for illuminated line-blanketed models with 3700K < T-eff < 7000K

The effect of mutual illumination in a close binary on the limb-darkening c oefficients is studied using the UMA (Uppsala Model Atmosphere) code in con vective Line-blanketed atmospheres illuminated by line-blanketed fluxes, fo r 3700 K less-than T-eff less-than 7000 K and 7000 K less-than T-h less-tha n 12000 K. The results show that the limb-darkening coefficients of illumin ated atmospheres are significantly different from the non-illuminated ones and mostly depend on four parameters: the amount of incident energy, the il lumination direction, the effective temperature of the illuminated star and the temperature of the illuminating one. We present bolometric, monochroma tic and passband specific coefficients and we give, for the latter, analyti cal expressions in order to easily account for the effect in light curve sy nthesis programs.