1. Ambartsumian V. A., 1944, Izv. Akad. Nauk ArmSSR, N 1, 2
2. Ambartsumyan V. A., 1960, Scientific Works, V. I, Yerevan,Izd. Acad. Nauk ArmSSR
3. Courant R., Hilbert D., 1962, Methods of Mathematical Physics, V. II
4. Mihalas D., 1978, Stellar atmospheres, San-Francisco, Freeman
5. Nikoghossian A. G., 1999, JQSRT, 61, 345