1. Moore, R. L., Hardebeck, H. E., Moffet, A. T. & Neff, D. Abstr. at U.S. National Radio Science Meet., Boulder (1983).
2. Masson, C. R. Astr. Astrophys. 114, 270–274 (1982).
3. dos Santos, P. M. & Lepine, J. R. D. Nature 278, 34–45 (1979).
4. Gardner, F. F. & Whiteoak, J. B. Mon. Not. R. astr. Soc. 201, 13P–15P (1982).
5. Churchwell, E. et al. Astr. Astrophys. 54, 969–971 (1977).