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Astron. Astrophys. 326, L37-L40 (1997)

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Letter to the Editor

On the possibility of a tidally excited low-frequency [FORMULA]-mode
in 51 Peg

B. Willems *, T. Van Hoolst **, P. Smeyers and C. Waelkens

Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200 B, B-3001 Heverlee, Belgium

Received 11 July 1997 / Accepted 8 August 1997

Abstract

The possibility of a resonant excitation of a free oscillation mode with an observed period of [FORMULA] 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 [FORMULA]-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 [FORMULA] for the radial velocity variations to be of the order of [FORMULA]. The probability for such a close resonance is less than [FORMULA]. 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.

Key words: Stars: oscillations - Stars: individual: 51 Peg

* Research Assistant of the Fund for Scientific Research - Flanders (Belgium) (F.W.O.)
** Postdoctoral Fellow of the Fund for Scientific Research - Flanders (Belgium) (F.W.O.). Present address: Koninklijke Sterrenwacht van Belgiï, Ringlaan 3, B-1180 Brussel, Belgium

Send offprint requests to: B. Willems

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© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998
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