A new method for the spectroscopic identification of stellar non-radial pulsation modes

I. The method and numerical tests

Institut für Astronomie der Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria e-mail: zima@ster.kuleuven.be

Received: 18 January 2006
Accepted: 27 March 2006

Abstract

Aims.We present the Fourier parameter fit method, a new method for spectroscopically identifying stellar radial and non-radial pulsation modes based on the high-resolution time-series spectroscopy of absorption-line profiles. In contrast to previous methods this one permits a quantification of the statistical significance of the computed solutions. The application of genetic algorithms in seeking solutions makes it possible to search through a large parameter space.

Methods.The mode identification is carried out by minimizing , using the observed amplitude and phase across the line profile and their modeled counterparts. Computations of the theoretical line profiles are based on a stellar displacement field, which is described as superposition of spherical harmonics and that includes the first order effects of the Coriolis force.

Results.We made numerical tests of the method on a grid of different mono- and multi-mode models for in order to explore its capabilities and limitations. Our results show that whereas the azimuthal order m can be unambiguously identified for low-order modes, the error of is in the range of . The value of m can be determined with higher precision than with other spectroscopic mode identification methods. Improved values for the inclination can be obtained from the analysis of non-axisymmetric pulsation modes. The new method is ideally suited to intermediatley rotating δ Scuti and β Cephei stars.