1. Belton , M. J. S. 1986.A precise spin period for P/Halley, 20th ESLAB Symp. Vol. 2, 599–603. ESA SP-250
2. Boice , D. C. 1990.A model of multigeneration neutrals in the cometary comae, Proc. of Workshop on Observations of Recent Comets(1990) Edited by: Huebner , W. F. 155–159.