1. A. A. Boyarchuk, “A Quantitative Analysis of the Chemical Composition of the Atmosphere of the Bright Component of β Lyrae,” Astron. Zh. 36(5), 766–777 (1959) [Sov. Astron. 3, 748 (1959)].
2. V. V. Holovatyi and B. Ya. Melekh, “The Chemical Composition of HII Regions in Blue Compact Dwarf Galaxies,” Astron. Zh. 82(9), 755–762 (2005) [Astron. Rep. 49, 779 (2005)].
3. V. V. Leushin, M. Yu. Nevskii, L. I. Snezhko, and V. V. Sokolov, “Hydrogen and Helium in the Visible Component of β Lyrae,” Astrofiz. Issled. (Izv. SAO) 9(1), 3–15 (1977).
4. L. S. Lyubimkov, “Evolution Changes of Helium Abundance in the Atmospheres of Stars of Early Spectral Classes,” Pis’ma Astron. Zh. 1(11), 29–31 (1975) [Sov. Astron. Lett. 1, 226 (1975)].
5. L. S. Lyubimkov, “Variations in the Helium Abundance in Associations and Clusters of O and B Stars,” Astrofizika 13(1), 139–151 (1977).