1. Albats, P., Frye, G. M., Zych, A. D., Mace, O. B., Hopper, V. D., and Thomas, J. A.: 1972,Nature 240, 221.
2. Ambartsumyan, V. A.: 1971,Astrofizika 7, 557.
3. Amnuel, P. R., Guseinov, O. Kh., and Kasumov, F. K.: 1972,Astrofizika 8, 561.
4. Bahcall, J. M. and Bahcall, N. A.: 1974, Proc. of the 16th Solvay Conf. onAstrophys. and Gravitation, ed. of the University of Brussels.
5. Bisnovatyi-Kogan, G. S. and Chechotkin, V. M.: 1973,Zh. Eksper-Teoret. Fiziki Pisma 17, 662.