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Astron. Astrophys. 336, 991-1006 (1998) AcknowledgementsWe thank Ted Bergin and James Deane for helpful discussions. We thank an anonymous referee for returning detailed comments, which refocused and greatly improved the quality of this paper. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1998 Online publication: July 27, 1998 ![]() |