1. Aizu, K 1987, this volume
2. Auriemma, C., Perola, G.C., Ekers, R., Fanti, R., Lari, C., Jaffe, W.J., Ulrich, M. H. 1977, Astron. and Astrophys 57, 41
3. Biermann, P., Eckart, A. and Witzel, A. 1985, Astron. Astrophys 142, L23
4. Condon J.J, Condon, M.A., Gisler, G., Puschell, J.J 1982, Astrophys. J 252, 102
5. Condon, J.J. 1984, Astrophys J. 287, 461