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Astron. Astrophys. 336, 662-666 (1998) AcknowledgementsWe are grateful to our referee, Dr. J. Guertler, for his constructive criticisms on a first version of this paper and to H. Aussel who made available to us the software to correct field distortion. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1998 Online publication: July 20, 1998 ![]() |