1. V. L. Afanas’ev, “Physical characteristics of the neutral coma of comet Abe, 1970 g,” Probl. Kosm. Fiz., No. 9, 120–129 (1974).
2. L. M. Shul’man, Dynamics of Comet Atmospheres. Neutral Gas (Naukova Dumka, Kiev, 1972) [in Russian].
3. M. F. A’Hearn, “Spectroscopy and spectrophotometry of comets at optical wavelength,” in Comets, Ed. by L. Wilkenning (Univ. of Arizona Press, Tucson, 1982), pp. 433–460.
4. M. F. A’Hearn, P. V. Birch, P. D. Feldman, et al., “Comet Encke–gas production and lightcurve,” Icarus 64, 1–10 (1985).
5. M. F. Hearn, R. C. Millis, D. O. Schleicher, et al., “The ensemble properties of comets: Results from narrowband photometry of 85 comets, 1976–1992,” Icarus 118, 223–270 (1995).