[en] We 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 spite of the assessed `subdwarf' status, and of the accurate distance determination from the Hipparcos data, the uncertainties in the metallicity and age, coupled with the uncertainty in the theoretical models, lead to a range of predictions on the oscillation frequency spectrum. Nevertheless, the determination of the ratio between the small separation in frequency modes, and the large separation as suggested by Roxburgh, provides a very good measure of the star age, quite independent of the metallicity in the assumed uncertainty range. In this range, the constraint on the dynamical mass and the further constraint provided by the assumption that the maximum age is 14 Gyr limits the mass of 85 Peg A to the range from 0.75 to 0.82M[SUB]solar[/SUB]. This difference of a few hundredths of a solar mass leads to well detectable differences both in the evolutionary stage (age) and in the asteroseismic properties. We show that the age determination which will be possible through the asteroseismic measurements for this star is independent either of the convection model adopted or the microscopic metal diffusion. The latter conclusion is strengthened by the fact that, although metal diffusion is still described in an approximate way, recent observations suggest that real stars suffer a smaller metal sedimentation compared with the models.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
D'Antona, F.; INAF, Osservatorio Astronomico di Roma, via Frascati 33, I-00040 MontePorzio, Italy
Cardini, D.; INAF, Istituto di Astrofisica Spaziale, via del Fosso del Cavaliere 100, I-00133 Roma, Italy
Di Mauro, M. P.; INAF, Osservatorio Astrofisico di Catania, via S. Sofia 78, I-95123 Catania, Italy
Maceroni, C.; INAF, Osservatorio Astronomico di Roma, via Frascati 33, I-00040 MontePorzio, Italy
Mazzitelli, I.; via Zambarelli 22, I-00044 Frascati, Italy
Montalban Iglesias, Josefa ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique stellaire théorique et astérosismologie
Language :
English
Title :
85 Peg A: what age for a low-metallicity solar-like star?
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