We acknowledge the support of NATO Collaborative Research Grant 941197. The necessary computing capacity was due to support from the Carlsberg Foundation. AB acknowledges support from the Danish Research Academy and the Danish Natural Science Research Council. CZ acknowledges partial support from NASA, Planetary Atmospheres Division. Valuable comments from Hollis R. Johnson are greatly appreciated.
© European Southern Observatory (ESO) 1997
Online publication: May 26, 1998