Asteroseismology in the Instability Strips

Research project P 14546 Asteroseismology in the Instability Strips Michael BREGER 09.10.2000 Our proposed project is to study asteroseismologically several different Delta Scuti and related stars. As with helioseismology, this requires us to detect many frequencies in our target objects; we intend to push the number of detected frequencies in previously studied stars to over 50 and for the "new" target 44 Tau to over 30 frequencies. In addition, we plan a multisite campaign on the cluster NGC 4755, which is known to contain 9 Beta Cephei stars. With CCD observations, all 9 Beta Cephei stars in this cluster can be studied simultaneously. In order to be able to model the frequencies which we observe, we need to have some independent constraints on the quantum numbers (n, I and in) of the observed individual pulsation modes. Thus, a subset of our observations on each object will be devoted to photometric and/or spectroscopic measurements which can be used for this "mode identification". We plan to obtain such mode identifications for over half of the observed frequencies. The final scientific step in our investigations is the theoretical modeling of the frequencies. By comparing the observed frequency ranges of excitation to the ranges predicted by nonadiabatic calculations, we can place constraints on the global parameters of these stars, such as their mass, luminosity, and chemical composition. In addition, by modeling the frequency spectra in detail, we hope to place tighter constraints on the models and to derive more information about the internal structure of these stars such as determining the amount of overshooting in the convective core and the rotation rate.