1. Bleeker, J. A. M. and Deerenberg, A. J. M.: 1970,Astrophys. J. 159, 215.
2. Bleeker, J. A. M., Burger, J. J., Deerenberg, A. J. M., Scheepmaker, A., Swanenburg, B. N., Tanaka, Y., Hayakawa, S., Makino, F., and Ogawa, H.: 1968,Can. J. Phys. 46, S461.
3. Davisson, C. M.: 1965,Alpha, Beta and Gamma-Ray Spectroscopy (ed. by K. Siegbahn), North-Holland Publ. Co., Amsterdam.
4. Hayakawa, S., Kato, T., Makino, F., Ogawa, H., Tanaka, Y., Yamashita, K., Matsuoka, M., Miyamoto, S., Oda, M., and Ogawara, Y.: 1969,IAU Symposium No. 37 (ed. by L. Gratton), D. Reidel Publ. Co., Dordrecht, The Netherlands.