1. Abbott, D. C. 1982, Ap. J., 263. 723.
2. Amett, W. D. 1987, Ap. J., 319, 136.
3. Ashworth, W.B. 1980, J. Hist. Astr., 11, 1.
4. Axelrod, T. S. 1980, Ph.D. thesis, University of California, Santa Cruz.
5. Badhwar, G. D. and Stephans, S. A. 1977, Ap. J., 212, 494.