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Astron. Astrophys. 336, L21-L24 (1998) AcknowledgementsWe thank K. Bischoff and P. Papaderos for useful comments. This work has been supported by DARA grant 50 OR94089 and DFG grant Ko 857/13-2.
© European Southern Observatory (ESO) 1998 Online publication: July 20, 1998 ![]() |