1. Allen, C.W.: 1973,Astrophysical. Quantities, 3rd ed., Athlone Press, London.
2. Auer, L.H. and Heasley, J.: 1976,Astrophys. J. 205, 165.
3. Bell, R.A., Eriksson, K., Gustafsson, B. and Nordlund, A.: 1976,Astron. Astrophys. Suppl. Ser. 23, 37.
4. Bell, R.A. and Gustafsson, B.: 1989,Mon. Not. R. Astron. Soc. 236, 653.
5. Crandall, D.H., Taylor, P.O. and Dunn, G. H.: 1974,Phys. Rev. A10, 141.