ON THE POSSIBILITY OF A TIDALLY EXCITED LOW-FREQUENCY G(-MODE IN 51-PEG())

The possibility of a resonant excitation of a free oscillation mode wi th an observed period of 4.2311 d in the star 51 Pegasi by the tidal a ction 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 h igh 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 esta blished by Smeyers et al. (in preparation) are used. For the numerical calculations, a standard solar model is used. It results that, in a f avourable case, the relative difference between the frequency of the t idally excited oscillation mode and the frequency of the resonant dyna mic tide must be smaller than 10(-8) for the radial velocity variation s to be of the order of 10 m s(-1). The probability for such a close r esonance is less than 10(-5). Since 51 Peg is not the only member of i ts 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.