1. Allen, C. W.: 1963, Astrophysical Quantities, 2nd Ed., Athlone Press, London.
2. Banos, G.: 1968, Ann. Astrophys. 31, 501.
3. Burger, H. C. and van Cittert, P. H.: 1932, Z. Phys. 79, 722.
4. Claas, W. J.: 1951, Rech. Obs. Astron. Utrecht 12, Part 1.
5. Corliss, C. H. and Bozman, W. R.: 1962, Natl. Bur. Std. Monograph No. 53.