KOUBSKÝ, Pavel, HARMANEC, Petr, HORN, Jiří, HUBERT, A. M., HUBERT, H., FLOQUET, M. 70 years of observations of 4 Herculis: Changes through three shell episodes. In: BALONA, L. A., HENRICHS, H. F., LECONTEL, J. M., eds. Pulsation, Rotation and Mass Loss in Early-Type Stars. Dordrecht: Kluwer Academic, 1994, s. 370-371.