Radial Pulsations in A Stars: the Effects of Opacity Fluctuations in their Atmospheres

We investigate the effect of pulsational opacity fluctuations in the atmospheres of A star models and show that the opacity fluctuations are responsible for the “bump” often seen in the temperature eigenfunctions in the region of the hydrogen ionization zone. We also present a formula that relates perturbations in the surface flux to those in effective temperature (Teff). This formula shows that for cooler A stars, opacity fluctuations can introduce a phase difference between δH(0)/H(0) and δTeff/Teff. In addition the new formula is used to calculate multicolour pulsational amplitudes that can be compared with photometric data to perform mode discrimination.