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Astron. Astrophys. 330, 1175-1179 (1998) AcknowledgementsSpecial thanks are due to A. D. Morse for advice and J. Gibson for technical assistance in methane analysis. The help of the irradiation group of compact cyclotron CV 28 of Nuclear Research Centre Jülich is gratefully acknowledged. The authors also wish to thank Thomas Stephan and an anonymous reviewer for their constructive remarks. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1998 Online publication: January 27, 1998 ![]() |