I should like to thank Dr. L.-Å. Nyman at SEST for giving me extra observing time (during maintenance), so that the map could be finished in one observing session with exceptional submillimetre weather. I am also grateful for very useful discussions with Drs. P. Bergman and P.O. Lindblad.
© European Southern Observatory (ESO) 1999
Online publication: March 1, 1999