1. V. A. Ambartsumyan, Astron. zh. 19, 30 (1942).
2. V. A. Ambartsumyan, ZhETF 13, 323 (1943).
3. V. V. Sobolev, Astron. zh. 26, 22 (1949).
4. S. Chandrasekhar, Astrophys. J. 103, 165 (1946); 104, 110 (1946); 104, 191 (1946); 105, 164 (1947).
5. S. Chandrasekhar, Radiative Energy Transfer [Russian translation], IL, Moscow (1953).