Astron. Astrophys. 323, 415-428 (1997)

Acknowledgements

We are grateful to H. DeWitt for pointing out the article of Boerker et al. (1982), to Dany Page and Yu.A. Shibanov for fruitful discussions, and to D. Page for reading the manuscript and making the most useful critical remarks. This work was supported in part by the RBRF grant No. 96-02-16870a, INTAS grant No. 94-3834, and DFG-RBRF grant No. 96-02-00177G. AYP gratefully acknowledges the hospitality of the theoretical astrophysics group of the Ecole Normale Supérieure de Lyon.

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

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