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Astron. Astrophys. 337, 962-965 (1998) AcknowledgementsThis work was supported in part by the Commission of the European Communities under Contracts ERBCHRXCT940604 and FMRX-CT98-0168. The authors are grateful to Bram Achterberg for helpful comments as a referee. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1998 Online publication: August 27, 1998 ![]() |