1. Cappellini, V.: 1986,Adv. Electronics Electro Phys. 56, Academic Press, New York.
2. Chandrasekhar, T., Ashok, N. M., Debi Prasad, C., and Desai, J. N.: 1988,Opt. Eng. 27, 67.
3. Debi Prasad, C., Chandrasekhar, T., Desai, J. N., and Ashok, N. M.: 1988,J. Astron. Astrophys. (in press).
4. Deharveng, L.: 1973,Astron. Astrophys. 41, 27.
5. Fabry, Ch. and Buisson, H.: 1911,Astrophys. J. 33, 406.