1. Allen, C. W.: 1973,Astrophysical Quantities, Athlone Press, London.
2. Banks, T. and Budding, E.: 1990,Astrophys. Space Sci. 167, 221.
3. Banse, K., Ponz, D., Ounnas, Ch., Grosbøl, P., and Warmels, R.: 1987, in L. B. Robinson (ed.),Instrumentation for Ground-based Optical Astronomy: Present and Future, 9th Santa Cruz Summer Workshop in Astron. Astrophys., Springer-Verlag, Berlin, p. 431.
4. Budding, E.: 1981, in F. D. Kahn (ed.),Investigating the Universe, D. Reidel Publ. Co., Dordrecht, Holland, p. 271.
5. Budding, E.: 1985,Publ. Astron. Soc. Pacific 97, 592.