Mode Identification and Seismic Modelling in the Cep Star EN (16) Lac

EN Lac was the first Cep star subjected to an asteroseismic analysis by (Dziembowski & Jerzykiewicz, 1996). The reason for choosing this star as a test case for asteroseismology is obvious: the star is a single-lined spectroscopic and an eclipsing binary with well-known orbital elements, which helps to constrain the physical parameters of the Cep-type primary. Moreover, the primary exhibits multiperiodic pulsations the periods of which have been studied in quite some detail in the literature and are known with an extremely high precision. However, general agreement on the mode identification was never reached. In fact, Dziembowski & Jerzykiewicz (1996) rejected some previously suggested identifications and used their theoretical modelling as mode identification tool in order to find overal full agreement between the observed variations and the excitation models. The seismic application remained limited, however, precisely due to the lack of unambiguous mode identifications.
Presently, all attempts to identify the modes are based upon multicolour photometry and/or radial-velocity measurements. In this paper, we perform first of all more accurate photometric mode identification by means of a new method developed by Dupret et al. (this conference) and based on non-adiabatic eigenfunctions. The latter are calculated in the outer atmosphere of the star. Secondly, we perform for the first time mode identification on the basis of the line-profile variations of EN Lac by means of a detailed analysis of 941 high-resolution high-signal-to-noise spectra of EN Lac, after having prewhitened the orbital motion. We do this by means of two different versions of the moment method (see poster by Briquet et al., this conference). We confront our results with those of Dziembowski & Jerzykiewicz (1996) and attempt a more in-depth seismic analysis of this young massive star.

 
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