Spectroscopic modelling of non-radial pulsation in rotating early-type stars

Abstract

A new computer model which simulates non-radial pulsations in rotating early-type stars is presented. The model constructs time-resolved synthetic spectra for a star undergoing multi-mode non-radial pulsation, using a rotationally distorted stellar grid and intrinsic spectral line profiles calculated from non-LTE model atmospheres. The treatment includes consideration of pulsation-induced velocity fields and temperature, surface-area and surface-normal perturbations. The effects of rotation on the pulsation modes of the star are considered by expressing the perturbed variables as linear combinations of terms proportional to spherical harmonics. Rotation acts to concentrate pulsational activity towards the stellar equator; this equatorial concentration, when combined with gravity darkening, leads to significant differences in the degree of line-profile variability between spectral lines formed at the equator and the pole, for both sectoral and tesseral modes. The rotation also leads to the existence of oscillatory quasitoroidal modes. The use of rotationally modified velocity fields and temperature perturbations leads to significant changes to the calculated line-profile variability. In contrast, the surface-area and surface-normal perturbations are the more important mechanisms for generating continuum variations, emphasizing the need for a proper treatment of these effects in the modelling of photometric variability.