A.F.J.M. thanks NSERC (Canada), FCAR (Québec), and the Killam program of the Canada Council for the Arts for financial support. T.E. is grateful for full financial aid from the Evangelisches Studienwerk/Germany which is supported by the German Government, as well as an extended bursary from the astronomy group at the Université de Montréal. Both authors acknowledge useful discussions with J.-F. Donati and G. Wade. We are grateful to M. Cohen, the referee, for useful comments.
© European Southern Observatory (ESO) 2000
Online publication: June 8, 2000