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Astron. Astrophys. 322, 633-645 (1997) AcknowledgementsThe computations in Sect. 3 were performed on the CRAY T-90 of the Zentralinstitut für Angewandte Mathematik, in Jülich, Germany. We acknowledge the constructive comments of the referee of this paper, B.T. Draine. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1997 Online publication: June 5, 1998 ![]() |