Effect of convective outer layers modeling on non-adiabatic seismic observables of delta Scuti stars

Context: The identification of pulsation modes in delta Scuti stars is mandatory for constraining the theoretical stellar models. The non-adiabatic observables used in the photometric identification methods depend, however, on convection modeling in the external layers. Aims: We determine how the treatment of convection in the atmospheric and sub-atmospheric layers affects the mode identification and what information about the thermal structure of the external layers can be obtained from amplitude ratios and phase lags in Strömgren photometric bands. Methods: We derive non-adiabatic parameters for delta Scuti stars by using, for the first time, stellar models with the same treatment of convection in the interior and in the atmosphere. We compute classical non-gray mixing length models, and as well non-gray ``full spectrum of turbulence'' (FST) models. Furthermore, we compute the photometric amplitudes and phases of pulsation by using the colors and the limb-darkening coefficients as derived from the same atmosphere models as used in the stellar modeling. Results: We show that the non-adiabatic phase-lag is mainly sensitive to the thermal gradients in the external layers, hence to the treatment of convection, and that this sensitivity is also clearly reflected in the multi-color photometric phase differences