Astronomy and Astrophysics, volume 291, 143-154 (1994/11-1)
Nonadiabatic observables in β Cephei models.
CUGIER H., DZIEMBOWSKI W.A. and PAMYATNYKH A.A.
Abstract (from CDS):
Using results of linear nonadiabatic calculations for oscillations of β Cephei star models, we calculate amplitudes and phases for light, colour and radial velocity for the unstable modes of low harmonic degrees, l. The nonadiabatic observables are the amplitude ratios and the phase differences for various oscillating parameters. We construct theoretical diagrams involving these observables as well as pulsation periods and compare them with the stellar data. Balona & 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 paricular, that the diagrams employing the satellite ultraviolet measurements are the best for discrimination between the l=0, 1 and 2 cases. The clearest separation of the domains for the three l-values occurs in the diagram making use of both photometric and the radial velocity data. 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 ratios diagrams in various photometric systems. The agreement is very satisfactory and, in most cases, the l-value can be determined. The nonadiabatic observables are useful not only to determine l but also the radial order of the observed modes as well as for constrain mean stellar parameters. As an example we consider the case of δ Ceti - a single mode β Cephei star. Our results point to the significant multicolour photometric and spectroscopic data for asteroseismology.