Spectroscopic nonadiabatic observables in Cephei models

Astronomical Institute of the Wrocław University, ul. Kopernika 11, 51-622 Wrocław, Poland

Corresponding author: H. Cugier, cugier@astro.uni.wroc.pl

Received: 4 May 2001
Accepted: 11 July 2001

Abstract

We calculate time sequences of Si III 455.26 nm line profiles for 10 models using results of the linear nonadiabatic calculations of Dziembowski & Pamyatnykh ([CITE]) for oscillations of β Cephei stars. The spectroscopic observables are amplitude ratios and phase differences for various oscillating parameters derived from line profiles. We search theoretical diagrams involving these observables for unstable modes with low harmonic degrees (, 1 and 2) and azimuthal orders of . We show that all unstable modes are grouped in domains assigned by different and m-values. In almost all studied diagrams, the retrograde (), prograde () and zonal () modes are well separated from each other. The clearest separation of the domains occurs for the m-values in the diagram making use of the first and second moments of line profiles. Neither the inclination angle i or the amplitude of the stellar radius variation ϵ change this conclusion. The diagram is however sensitive to the equatorial velocity v_e of the star. The method of determination of m is valid and efficient for the equatorial rotational velocity km . The observables studied here are usually by-products of periodogram analyses of time series of observed characteristics of line profiles. Our results point to the significance of such data for asteroseismology in addition to measurements of oscillation frequencies and photometric nonadiabatic observables.