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139P/Väisälä-Oterma

Past, Present, and Future Orbits by Kazuo Kinoshita

A. Nakamura photo of 139P exposed on 1998 December 17
Copyright 1998 by Akimasa Nakamura

The CCD image was taken at Kuma Kogen Astronomical Observatory on 1998 December 17, using a 0.60-m f/6 Ritchey-Chretien telescope.

Discovery

     The discovery of this comet was a long time coming. During a routine asteroid search program at Turku, Yrjö Väisälä found this object on 1939 October 7.91 in Aries. The object was classed as an asteroid and designated 1939 TN. The magnitude was determined as 15.8. The object was further photographed on October 18.88 and 20.85. The fourth and final observation came on November 11.74. Precise positions were not published until 1979 and an orbit calculation by Liisi Oterma suggested the object was a comet. In addition, she communicated to the Central Bureau for Astronomical Telegrams in 1981 that a reexamination of the plates suggested the object was somewhat diffuse.
     The LINEAR program discovered an apparent asteroidal object on 1998 November 18.26. Three additional positions were obtained on the 18th and three more were obtained on November 21. The object was given the asteroidal designation 1998 WG22. S. Nakano subsequently noted the orbit was similar to that of 1939 TN, and he successfully linked the two apparitions. D. Balam (Dominion Astrophysical Observatory) observed the object on December 6.3 using a 1.8-m reflector and noted a coma 8 arc seconds across and a tail extending 18 arc seconds toward PA 260 degrees.

Historical Highlights

  • S. Nakano computed the first orbit linking the 1939 and 1998 apparitions. For the latter he determined the perihelion date as 1998 September 27.26, the perihelion distance as 3.39 AU, and the orbital period as 9.55 years.
  • Integration of the motion of this comet indicates it passed only 0.18 AU from Jupiter during 1935 May, and then passed 1.07 AU from that planet during 1981 August and 1.10 AU away during 1995 November.
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