1. Adams, D. J., Janes, A. F., and Whitford, C. H.: 1972, Astron. Astrophys. 20, 121.
2. Adler, I., Trombka, J., Gerard, J., Lowman, P., Schmadebeck, R., Blodget, H., Eller, E., Yin, L., Lamothe, R., Gorenstein, P., and Bjorkholm, P.: 1972, Science
175, 436.
3. Allen, C. W.: 1963, Astrophysical Quantities, 2nd ed., The Athlone Press, London, p. 233f.
4. Angel, J.R.P., Novick, R., Van den Bout, P., and Wolff, R.: 1969, Phys. Rev. Letters
22, 861.
5. Angel, J.R.P. and Weisskopf, M.C.: 1970, Astron. J. 75, 231.