We should like to thank the Director and Staff of the Canada-France-Hawaii-Telescope Corporation for making possible the observations reported in this paper. We should also like to acknowledge the assistance of the Particle Physics and Astronomy Research Council (UK) and the CNRS for financial assistance for one of us (DF). The involvement of JLL, SL and FR was partially supported by the "Programme Physique et Chimie du Milieu Interstellaire du CNRS".
© European Southern Observatory (ESO) 1998
Online publication: April 15, 1998