1. Aizu, K. 1973, Prog. Theoret. Phys., 49, 1184.
2. Anderson, C.M., Cassinelli, J.P., and Sanders, W.T. 1981, Ap. J. J. Lett., 247, L127.
3. Anzer, U., Borner, G., and Monaghan, J.J. 1987, Astron. Ap., 176, 235.
4. Baize, P. 1980, Astron. Ap. Suppl., 39, 83.
5. Bondi, H. 1952, M.N.R.A.S., 114, 195.