New grids of ATLAS9 atmospheres. II. Limb-darkening coefficients for the Strömgren photometric system for A-F stars

Using up-to-date model atmospheres (Heiter et al. \cite{Heiter02}) with the turbulent convection approach developed by Canuto et al. (\cite{Canuto96}, CGM), quadratic, cubic and square root limb darkening coefficients (LDC) are calculated with a least square fit method for the Strömgren photometric system. This is done for a sample of solar metallicity models with effective temperatures between 6000 and 8500 K and with log g between 2.5 and 4.5. A comparison is made between these LDC and the ones computed from model atmospheres using the classical mixing length prescription with a mixing length parameter alpha =1.25 and alpha =0.5. For CGM model atmospheres, the law which reproduces better the model intensity is found to be the square root one for the u band and the cubic law for the v band. The results are more complex for the b and y bands depending on the temperature and gravity of the model. Similar conclusions are reached for MLT alpha =0.5 models. As expected much larger differences are found between CGM and MLT with alpha =1.25. In a second part, the weighted limb-darkening integrals, b_l, and their derivatives with respect to temperature and gravity, are then computed using the best limb-darkening law. These integrals are known to be very important in the context of photometric mode identification of non-radial pulsating stars. The effect of convection treatment on these quantities is discussed and as expected differences in the b_l coefficients and derivatives computed with CGM and MLT alpha =0.5 are much smaller than differences obtained between computations with CGM and MLT alpha =1.25.

Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/1095