1. Abramenkov, E.A. and Krymkin, V.V.: 1982, AZh., 59, 263; 1983, AZh., 60, 53; 1992a, AZh., 69, 489; 1992b, AZh., 69, 731.
2. Akujor, C.E., Spencer, R.E. and Wilkinson, P.N.: 1990, MNRAS 244, 362.
3. Braude, S.Ya.: 1965, AZh., 42, 1150.
4. Braude, S.Ya., Lebedeva, O.M., Megn, A.V., Ryabov, B.P. and Zhuck, I.N.: 1969, UkFiz 14, 1761.
5. Braude, S.Ya. and Megn, A.V.: 1997, KFNT. 13, 74.