1. ‘Temporary satellite capture and orbital evolution of comet P/Helin-Roman-Crockett’;Tancredi;Astron. Astrophys.,1990
2. Cometary dynamics
3. Recent Dynamical History of the Six Short-Period Comets Discovered in 1975
4. ‘The structure of the cloud of comets surrounding the solar system and a hypothesis concerning its origin’;Oort;Bull. Astron. Inst. Neth.,1950
5. Nakamura T. , and Yoshikawa M. : 1991, ‘Comet P/Helin: a comet to be ejected out of the Solar System?’, preprint