1. Adams, W.S., Merrill, P.W., et al., 1957, Astrophysical Journal, 125, 102
2. Conti, P., 1972 Astrophysical Journal, 174, L79
3. de Groot, M., 1969, Bulletin of the Astronomical Institutes of the Netherlands, 20, 225
4. Guinan, E.F., McCook, G.P., Harris, W.T., Speranzini, D., Wacker, S.W., 1985, Information Bulletin on Variable Stars, 2762
5. Lamers, H.J.G.L.M., Korevaar, P., Cassatella, A., 1985, Astronomy and Astrophysics, 149, 29