1. Allen, C. W.: 1963, Astrophysical Quantities, 2nd ed., The Athlone Press, London.
2. Babcock, H. D.: 1945, Astrophys. J. 102, 154.
3. Baschek, B., Holweger, H., and Traving, G.: 1966, Abhandl. Hamburger Sternwarte VIII, Nr. 1.
4. Bergström, I., Bromander, J., Buchta, R., Lundin, L., and Martinson, I.: 1969, Phys. Letters 28A, 721.
5. Bernas, R., Gradsztajn, E., Reeves, H., and Schatzman, E.: 1967, Ann. Phys. 44, 426.