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Astron. Astrophys. 324, 51-64 (1997) AcknowledgementsWe thank R. Lucas and H. Liszt for communicating Galactic column density data prior to publication. TW acknowledges support from the Swedish Natural Science Council (NFR) for this research. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1997 Online publication: May 26, 1998 ![]() |