1. Allen, C. W.: 1976,Astrophysical Quantities, 3rd edition with corrections, University of London, The Athlone Press, London.
2. Barbon, R., Ciatti, F., and Rosino, L.: 1973,Astron. Astrophys. 25, 241.
3. Barbon, R., Ciatti, F., and Rosino, L.: 1979,Astron. Astrophys. 72, 287.
4. de Vaucouleurs, G.: 1980,Publ. Astron. Soc. Pacific 92, 579.
5. Gry, C., Cassatella, A., Wamsteker, W., Sanz, L., and Panagia, N.: 1987,IAU Circ., No. 4324.