1. L. V. Mirzoyan, in: Early Stages in the Evolution of Stars [in Russian], Naukova Dumka, Kiev (1977), p. 100.
2. G. V. Zaitseva, Peremennye Zvezdy,16, 435 (1968).
3. G. V. Zaitseva, V. M. Lyutyi, and A. M. Cherepashuk, Astrofizika,10, 357 (1974).
4. W. Wenzel, in: Non-Periodic Phenomena in Variable Stars, IAU Colloq., Budapest (1969). p. 61.
5. W. Wenzel, MVS,5, 75 (1970).