A PHOTOMETRIC-STUDY OF BETA-CEPHEI STARS .2. DETERMINATION OF THE DEGREES-L OF PULSATION MODES

The wavelength dependence of photometric amplitudes is used as a means of identifying the degrees l of pulsation modes of beta Cephei stars studied in an earlier paper. To this end, an expression for the photom etric amplitude of a non-rotating pulsating star is derived in terms o f the wavelength of the radiation received and the degree of the pulsa tion mode involved. The derivation differs from earlier derivations in that the specific radiation intensity is considered instead of the ou tward normal radiation flux. Furthermore, the effects of the non-radia l components of the Lagrangian displacement on the local surface eleme nt of the star are taken into account. The angular dependence of the s pecific radiation intensity is determined by a limb-darkening function . The relative Lagrangian perturbation of the specific radiation inten sity is set equal to the relative Lagrangian perturbation of the outwa rd normal radiation flux. The physical parameters of the beta Cephei s tars are estimated by means of calibrations of photometric systems. Fr om a comparison of the calibrations of the Walraven, the Geneva, and t he Stromgren system for early-type stars, it appears that the most rel iable values are obtained by means of the Walraven system. The influen ce of the uncertainties on the physical parameters on the determinatio n of the degrees l of pulsation modes in beta 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 fitt ing curves of the wavelength dependences of theoretical photometric am plitudes for various degrees e to the wavelength dependence of observa tionally determined photometric amplitudes. In this way, values for th e degrees l of most of the pulsation modes of the beta Cephei stars co nsidered are found. It appears that not all beta Cephei stars pulsate in at least one radial mode and that multiperiodic beta Cephei stars p ulsate in a variety of combinations of pulsation modes.