1. A’Hearn, M. F., Feldman, P. D., and Schleicher, D. G. 1983, Astrophys. J. 274, pp. L99 - L103.
2. Feldman, P. D., A’Hearn, M. F., and Millis, R. L. 1984, Astrophys. J. 282, pp. 799 - 802.
3. Morris, C. S. and Green, D. W. E. 1983, Bull. Amer. Astr. Soc. 15, p. 803.
4. Morris, C. S. and Green, D. W. E. 1983, Bull. Amer. Astr. Soc. 15, p. 803.
5. Duley, W. W., Millar, T. J., and Williams, D. A, 1980, Mon. Not. Roy. Astr. Soc. 192, pp. 945 - 957.