MAT would like to thank PPARC for their support via a studentship and the JCMT staff for all their assistance during the observations. We would like to thank an anonymous referee for making several suggestions which substantially improved the content of this paper. Astrophysics research at the University of Kent and UMIST is supported via grants from PPARC.
© European Southern Observatory (ESO) 1999
Online publication: February 23, 1999