We are grateful to G. Alecian, Y. Lebreton and R. Cayrel for helpful discussions and communicating their work before publication. We would also like to thank the referees, Drs. S. Degl'Innocenti and Dr. V. Castellani, for their careful review of this paper and for a number and useful suggestions. This work was partly supported by the GDR G131 "Structure Interne des Etoiles et des Planètes géantes" of CNRS (France). Most of this work has been performed using the computing facilities provided by the OCA program "Simulations Interactives et Visualisation en Astronomie et Mécanique (SIVAM)".
© European Southern Observatory (ESO) 1999
Online publication: April 12, 1999