Using Balmer line profiles to investigate convection in A and F stars

Balmer lines are an important diagnostic of stellar atmospheric structure, since they are formed at a wide range of depths within the atmosphere. The different Balmer lines are formed at slightly different depths making them useful atmospheric diagnostics. The low sensitivity to surface gravity for stars cooler than ~8000 K makes them excellent diagnostics in the treatment of atmospheric convection. For hotter stars Balmer profiles are sensitive to both effective temperature and surface gravity. Provided we know the surface gravity of these stars from some other method (e.g. from eclipsing binary systems), we can use them to determine effective temperature. In previous work, we have found no significant systematic problems with using uvby photometry to determine atmospheric parameters of fundamental (and standard) stars. In fact, uvby was found to be very good for obtaining both Teff and log g. Using Halpha and Hbeta profiles, we have found that both the Canuto & Mazzitteli and standard Kurucz mixing-length theory without approximate overshooting are both in agreement to within the uncertainties of the fundamental stars. Overshooting models were always clearly discrepant. Some evidence was found for significant disagreement between all treatments of convection and fundamental values around 8000~9000K, but these results were for fundamental stars without fundamental surface gravities. We have used stars with fundamental values of both Teff and log g to explore this region in more detail.