1. See e.g. Radio Astronomy, John D. Kraus, Cygnus-Quasar Books, 2nd edition (1986).
2. Masson C. R.: 1982, Astron. Astrophys. 114, 270.
3. Piciorgros, A.: 1988, Ph.D. Thesis, University of Cologne.
4. Rau, G., Schieder, R., and Vowinkel, B.: 1984, Proc. 14th European Microwave Conf., Liege.
5. Schieder, R., Vowinkel, B., and Rau, G.: 1985, Proc. SPIE Conf. on Submillimeter Spectroscopy, Cannes, 598.