I would like to acknowledge useful discussions with John Carlstrom and Bill Holzapfel. I would also like to thank the two referees, Mark Birkinshaw and an anonymous referee, for detailed comments on the manuscript. This study was partially supported by the McCormick Fellowship at the University of Chicago, and a Grant-In-Aid of Research from the National Academy of Sciences, awarded through Sigma Xi, the Scientific Research Society.
© European Southern Observatory (ESO) 1998
Online publication: October 21, 1998