p-mode oscillations of ![](../../images/alpha.png) -Cen A: the need for space asterosismology
A.Thoul, R.Scuflaire, B.Vatovez, A.Noels
Département d'Astrophysique et de Géophysique,
Université de Liège, Allée du 6 août, Bât. B5c,
B-4000, Liège, Belgium
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
![](../../images/deltam.png) = (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
![](../../images/deltam.png) = (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 ![](../../images/deltam.png) vary with , but the variations are below the
ground-space resolution obtained by Bouchy and Carrier (2001) and the small spacings ![](../../images/delta.png)
will give us information on the stellar core, but are again below the
ground-space resolution. Both the variations of ![](../../images/deltam.png) with and the values of
![](../../images/delta.png) vary from model to model. If measured, they will give us invaluable information
about the observed stars
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Last changed: 2002/Jun/04
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