We thank B.M. Lasker for digitizing the photographic plates; G. Massone and L. Lanteri for their help with the ground based observations and plate mesurements. Finally, we wish to thank Dr. L.V. Morrison for his careful refereeing.
A.C. acknowledges financial support from the ST ScI grants GO-4666 and GO-3594.
© European Southern Observatory (ESO) 1997
Online publication: July 3, 1998