A photometric study of β Cephei stars. II. Determination of the degrees l of pulsation modes.
HEYNDERICKX D., WAELKENS C. and SMEYERS P.
Abstract (from CDS):
The wavelength dependence of photometric amplitudes is used as a means of identifying the degrees l of pulsation modes of β Cephei stars studied in an earlier paper. To this end, an expression for the photometric amplitude of a non-rotating pulsating star is derived in terms of the wavelength of the radiation received and the degree of the pulsation mode involved. The derivation differs from earlier derivations in that the specific radiation intensity is considered instead of the outward normal radiation flux. Furthermore, the effects of the non-radial components of the Lagrangian displacement on the local surface element of the star are taken into account. The angular dependence of the specific radiation intensity is determined by a limb-darkening function. The relative Lagrangian perturbation of the specific radiation intensity is set equal to the relative Lagrangian perturbation of the outward normal radiation flux. The physical parameters of the β Cephei stars are estimated by means of calibrations of photometric systems. From a comparison of the calibrations of the Walraven, the Geneva, and the Stroemgren system for early-type stars, it appears that the most reliable values are obtained by means of the Walraven system. The influence of the uncertainties on the physical parameters on the determination of the degrees l of pulsation modes in β Cephei stars is examined. The expression for the photometric amplitude of a pulsating star is used for the determination of the degree l of a pulsation mode by fitting curves of the wavelength dependences of theoretical photometric amplitudes for various degrees l to the wavelength dependence of observationally determined photometric amplitudes. In this way, values for the degrees l of most of the pulsation modes of the β Cephei stars considered are found. It appears that not all β Cephei stars pulsate in at least one radial mode and that multiperiodic β Cephei stars pulsate in a variety of combinations of pulsation modes.
stars: early-type - stars: fundamental parameters - Hertzsprung-Russell (HR) diagram - stars: oscillations - stars: variables: other