1. Allen, C.W. 1973, Astrophysical Quantities, Athlone Press.
2. Brancewicz, H.K. and Dworak, T.Z. 1980, Acta Astron., 30, 501.
3. Budding, E 1980, IAU Symp. No. 88, ed. M. Plavec et al., Reidel, p.299.
4. Budding, E. 1981a, Investigating the Universe, ed. F.D. Kahn, Reidel, p. 271.
5. Budding, E. 1984a, Bull. Inf. Centre d. Donn. Stell., 27, 91.