1. Lovell, B., Nature, 222, 1126 (1969).
2. Lovell, B., Q. Jl R. astr. Soc., 12, 98 (1971).
3. Higgins, C. S., Solomon, L. H., and Bateson, F. M., Aust. J. Phys., 21, 725 (1968).
4. Chugainov, P. F., IAU Inf. Bull. on Variable Stars No. 605 (1971).
5. Johnson, H. L., Annls Astrophys., 18, 292 (1955).