1. Allen, C. W.: 1972, Astrophysical Quantities, 2nd ed., The Athlone Press, London.
2. Altschuler, M. D., Lillienquist, C. G., and Nakagawa, Y.: 1969, Solar Phys. 5, 366.
3. Beckers, J. M.: 1964, Ph.D. Thesis, Utrecht.
4. Cao, T. J., Xu, A. A., and Tang, Y. H.: 1979, Acta Astron. Sinica 20, 143.
5. Ding, J. P. and Xu, A. A.: 1984, Chinese J. Space Sci. 4, 89.