We thank Leonardo Vanzi for his help during observations, Sandro Gennari and the LONGSP/TIRGO staff for their help in this project. We are indebted to Frank Bertoldi, Tino Oliva and Malcolm Walmsley for many interesting discussions on the various aspects of this work. The theoretical project on time-dependent PDR was partly supported by ASI grants 92-RS-54, 94-RS-152, ARS-96-66 to the Osservatorio di Arcetri. Support from C.N.R.-N.A.T.O. Advanced Fellowship program and from NASA's Origins of Solar Systems program (through grant NAGW-4030) is gratefully acknowledged.
© European Southern Observatory (ESO) 1999
Online publication: February 23, 1999