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Solar-type stars

M. P. Di Mauro in collaboration with F. D'antona and C. Maceroni of the Astronomical Observatory of Monte Porzio Catone (Rome) and D. Cardini of the institute IASF of Rome has been working during the 2004 on the preparation of an article in which the authors (D'antona, Cardini, Di Mauro, Maceroni, Mazzitelli in preparation) explore the possible evolutionary status of the primary component of the binary 85 Pegasi, listed as a target for asteroseismic observations by the MOST satellite. In fact, 85 Peg A can be considered as a good candidate for asteroseismic studies, since theory predicts presence of oscillations, similarly to those observed in the Sun, excited stochastically by turbulent convection with a detectable surface amplitude of oscillation. Stellar models, produced employing the Aton 3.0 version of the Aton code (Mazzitelli 1979), indicate that this star is in the main-sequence phase of evolution, with a mass in the range $M=0.75-0.82 M_{\odot}$ and with an age which can varies from $8$ to $14 \mathrm{Gyr}$. These values have been obtained by assuming the most recent observational parameters of temperature and luminosity.

Unfortunately, the classical method of fitting the stellar modeling parameters to the observational data does not allow to reduce the uncertainty on the determination of age and mass. In spite of the assessed `subdwarf' status, and of the accurate distance determination from the Hipparcos data, the uncertainties in the metallicity and age of this star, coupled with the uncertainty in the theoretical models, lead to a range of predictions about the oscillation frequency spectrum.

The authors demonstrate, from the analysis of the theoretical oscillation spectra, calculated on the structure models, that observations of oscillation frequencies of this star can provide a very good measure of the star's age, quite independent of the metallicity in the assumed uncertainty range. In fact, a difference of a few tenths in solar mass corresponds to a well detectable difference both in the evolutionary stage and in the asteroseismic properties. It can be concluded that a great hope exists that observations of oscillation frequencies of 85 Peg provided by the MOST satellite will allow to determine the age of this subdwarf. Therefore, it will be possible to put a lower limit to the age of the old galactic stars, and hence to the age of the Galaxy.


next up previous contents index
Next: Asteroseismic techniques Up: Stellar oscillations and asteroseismology Previous: Stellar oscillations and asteroseismology   Contents   Index
Innocenza Busa' 2005-11-14