1. Allen, C. W.: 1976,Astrophysical Quantities, Athlone Press, London, p. 200.
2. Baade, D.: 1981, in G.E.V.O.N. and C. Sterken (eds.),Proc. of Workshop on Pulsating B stars, Nice Obs., p. 267.
3. Barbier, D. and Chalonge, D.: 1941,Ann. Astrophys. 4, 30.
4. Beeckmans, F.: 1976,Astron. Astrophys. 49, 263.
5. Blanco, V. M., Demers, S., Douglass, G. G., and Fitzgerald, M. P.: 1968,Photoelectric Catalogue 21, Publ. United States Naval Obs., 2nd series, Washington.