p-mode oscillations of -Cen A: the need for space asterosismology

The binary system -Cen A-B provides an excellent testbed to probe the internal structure of solar-like stars. The luminosity, effective surface temperature, chemical composition, and mass of both components are known with very good accuracy. Both stars can be modelled through stellar evolution codes; since they form a binary it can be assumed that they have the same age and the same chemical composition, thus providing additional constraints for the models. Guenther & Demarque (2000) and Morel et al. (2000) have analyzed the -Cen system thoroughly. Since then, Bouchy & Carrier (2001) have detected the p-mode oscillations of -Cen A.
We have revisited the -Cen binary system, using the latest observations. Using CLES (Code Liégeois d'Evolution Stellaire) we have calculated models for the two components A and B, using the latest values for the luminosities, effective temperatures, masses, and chemical composition, and including all the uncertainties on these values. We have also calculated the p-mode oscillations of -Cen A using OSC (the Lièege Stellar Oscillation Code, see Boury et al., 1975).
For each of these models we can fit perfectly the calculated p-mode oscillation spectrum to the observations. This result confirms what has been already pointed out by Guenther and Demarque (2000), i.e., the fact that the large frequency spacing =(n,l)-(n-1,l) where n and l are the radial and azimuthal mode numbers respectively, is primarily influenced by the stellar radius, i.e. its luminosity, and much less by its chemical composition. Unfortunately, the small frequency spacing =(n,l)-(n-1,l+2) is of the order of the resolution of the observations quoted by Bouchy and Carrier (2001).
We also show that the frequency spectrum obtained by Bouchy and Carrier is flawed by the 1-day and the 2-day aliases, which give unphysical large amplitude peaks in the oscillation spectrum, making it difficult to identify the real peaks, and certainly masking any possible detection of l=2 peaks.
Asterosismology space missions will give us oscillation spectra without aliases, and with a resolution that should help us identify the stars parameters and internal structure. Indeed, the large spacings vary with , but the variations are below the ground-space resolution obtained by Bouchy and Carrier (2001) and the small spacings will give us information on the stellar core, but are again below the ground-space resolution. Both the variations of with and the values of vary from model to model. If measured, they will give us invaluable information about the observed stars

 
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