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117P/Helin-Roman-Alu 1

Past, Present, and Future Orbits by Kazuo Kinoshita

A. Nakamura image of 117P obtained on 1997 July 5
Copyright © 1997 by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan)

The CCD image was taken on 1997 July 5.72, using a 0.60-m f/6 Ritchey-Chretien telescope.


     Eleanor F. Helin, Brian P. Roman, and Jeff Alu (Palomar Observatory, California, USA) discovered this comet on images obtained with the 0.46-m Schmidt telescope on 1989 October 2.42 and 2.44. They described as diffuse with some condensation, and estimated the magnitude as 17.5. They confirmed the comet on October 5 and 6.

Historical Highlights

  • Using the initial five positions from October 2 to 6, Daniel W. E. Green of the Central Bureau for Astronomical Telegrams computed and published a parabolic orbit on October 6 indicating a perihelion date of 1989 April 20, a perihelion distance of 2.22 AU, and an inclination of 6.5 degrees. He added that it was likely this was a short-period comet.
  • On 1989 October 13, the Central Bureau announced that Helin had found two prediscovery images from September 7.44 and 8.41. The comet's magnitude was estimated as 16.5 and a slight tail was extending toward the west-southwest.
  • The prediscovery images, as well as images acquired elsewhere up to October 10, enabled Green to confirm the comet was moving in a short-period orbit. The elliptical orbit indicated the perihelion had actually occurred on 1987 November 8. The perihelion distance was given as 3.67 AU, and the orbital period was given as 9.64 years. Green added that this orbit was still somewhat indeterminate. Ultimately, it turned out the perihelion distance was 1987 October 12 and the orbital period was 9.50 years.
  • Ultimately, prediscovery images were found from 1988 August 10.38, 10.40, and 12.39, when it was photographed with the 0.46-m Schmidt at Palomar.
  • The comet was only followed until 1989 December 1.15, when Palomar astronomers photographed it with the 1.5-m telescope and estimated the magnitude as 17.5.
  • James V. Scotti (Steward Observatory, Kitt Peak, USA) detected the comet with a 0.91-m telescope on 1993 January 24.34, when it was near aphelion. The magnitude was given as 21.2 and the comet was then 5.25 AU from the sun. This showed the comet was visible throughout its orbit.
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