Astronomy and Astrophysics, volume 326, L37-40 (1997/10-3)
On the possibility of a tidally excited low-frequency g+-mode in 51 Peg.
WILLEMS B., VAN HOOLST T., SMEYERS P. and WAELKENS C.
Abstract (from CDS):
The possibility of a resonant excitation of a free oscillation mode with an observed period of 4.2311d in the star 51 Pegasi by the tidal action of a low-mass companion is investigated. A free oscillation mode with the observed period is shown to correspond to a g+-mode of a high radial order. For the determination of the tidal displacement in a component of a close binary system of stars near resonance between a dynamic tide and a free oscillation mode of the star, expressions established by Smeyers et al. (in preparation) are used. For the numerical calculations, a standard solar model is used. It results that, in a favourable case, the relative difference between the frequency of the tidally excited oscillation mode and the frequency of the resonant dynamic tide must be smaller than 10–8 for the radial velocity variations to be of the order of 10m/s. The probability for such a close resonance is less than 10–5. Since 51 Peg is not the only member of its class, it then seems unlikely that forced oscillations caused by a low-mass companion are responsible for the radial velocity variations that were reported for 51 Peg.