NONADIABATIC OBSERVABLES IN BETA-CEPHEI MODELS

Using results of linear nonadiabatic calculations for oscillations of beta Cephei star models, we calculate amplitudes and phases for light, colour and radial velocity for the unstable modes of low harmonic deg rees, l. The nonadiabatic observables are the amplitude ratios and the phase differences for various oscillating parameters. We construct th eoretical diagrams involving these observables as well as pulsation pe riods and compare them with the stellar data. Balona and Stobie (1979) showed that the diagrams based on two-colour photometric data may be used to determine the l-value of an observed mode. Our use of results of nonadiabatic calculations improves their method. We show, in paricu lar, that the diagrams employing the satellite ultraviolet measurement s are the best for discrimination between the l = 0, 1 and 2 cases. Th e clearest separation of the domains for the three l-values occurs in the diagram making use of both photometric and the radial velocity dat a. The observational points fall into three theoretical domains and an assignment of the l-value is unambiguous. A comparison of the theory with the observations is also made using the Period versus Amplitude r atios diagrams in various photometric systems. The agreement is very s atisfactory and, in most cases, the l-value can be determined. The non adiabatic observables are useful not only to determine l but also the radial order of the observed modes as well as for constrain mean stell ar parameters. As an example we consider the case of delta Ceti - a si ngle mode beta Cephei star. Our results point to the significant multi colour photometric and spectroscopic data for asteroseismology.