1. K. Kawabata, Publ. Astron. Soc. Jpn.,16, 30 (1964).
2. V. N. Sazonov and V. N. Tsytovich, Radiofizika,11, 1287 (1968).
3. V. V. Zheleznyakov, Astrophys. Space Sci.,2, 403 (1968).
4. V. V. Zheleznyakov, E. V. Suvorov, and V. E. Shaposhnikov, Astron. Zh.,51, 243 (1974).
5. V. N. Sazonov, Astrofizika,10, 405 (1974).