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168P/Hergenrother

Past, Present, and Future Orbits by Kazuo Kinoshita

M. Jäger photo of 168P exposed on 1999 January 13
Copyright © 2012 by Michael Jäger (Austria)

The CCD image was taken on 2012 October 3.83, using a 25-cm reflector. Michael acquired ten 130-second exposures using an L filter and three 180 second exposures using RGB filters. These were all combined to form this image.

Discovery

     C. W. Hergenrother discovered this comet on CCD images obtained by T. B. Spahr with the 0.41-m f/3 Schmidt telescope in the course of the Catalina Sky Survey on 1998 November 21.10. An additional image obtained on November 21.12 showed the comet moving northeastward. He estimated the magnitude as 17.3 and said the comet was moderately condensed with a broad tail extending 30-60 arcsec toward PA 80°. Additional images were obtained on November 22.

T. B. Spahr images of 168P exposed on 1998 November 21
Copyright © 1998 by Catalina Sky Survey, University of Arizona

These images were taken by T. B. Spahr on 1998 November 21. He used a 0.41-m Schmidt telescope. These were the images Hergenrother first discovered the comet on. Note that in the first frame, the comet was partially covered by the vertical line cutting through the image.


Historical Highlights

  • The first orbit released for this comet was a parabolic one computed by Brian G. Marsden (Central Bureau for Astronomical Telegrams) and published on IAU Circular 7057 (1998 November 23). Based on positions gathered during the period of 1998 November 21 to 23, he determined the perihelion date as 1998 November 26.13 and the perihelion distance as 1.56 AU. The low inclination prompted Marsden to suggest the comet was "probably of short period." On December 18 the Central Bureau issued MPEC 1998-Y15. It indicated that further observations had confirmed Marsden's suggestion that the comet was moving in a short-period orbit. Based on 37 positions obtained during the period of November 16 to December 17, Marsden determined a perihelion date of 1998 December 6.06, a perihelion distance of 1.42 AU, and an orbital period of 6.78 years.
  • Initial observations soon after discovery indicated the comet was around magnitude 17.5. With the comet passing perihelion in early December it began fading as its distance from Earth also increased. By mid-December the brightness had declined to magnitude 18 and it reached 19 by mid-February of 1999. It was last detected on April 15.14 by observers at the Catalina Station (Tucson), at which time the magnitude was given as fainter than 20.
  • Following the final observations of this comet, Patrick Rocher refined the orbit of this comet. Rocher used 76 positions obtained between 1998 November 21 and 1999 April 15 and determined the perihelion date as 1998 December 5.946, the perihelion distance as 1.420 AU, and the orbital period as 6.906 years. He estimated the period's uncertainty as ±0.1436 day.
  • APPARITION OF 2005
    [Perihelion Date=2005 November 2.47; Period=6.92 years]
  • K. Kinoshita and S. Nakano independently used positions spanning the entire 1998 apparition to predict the comet's next perihelion date. Kinoshita determined a date of 2005 November 2.19 on August 13, 2000, while Nakano determined the date as 2005 November 2.17 on May 8, 2002. This comet was recovered by D. Herald (near Canberra, Australia) using his 36-cm reflector and a CCD camera. The comet appeared on several images acquired on 2005 July 4 and July 5. The nuclear magnitude was within the range of 19.4-20.7. Herald said a stack of fifteen 5-minute exposures revealed a tail extending 20 arcmin toward PA 270°. The recovery revealed that the comet's actual perihelion date was 2005 November 2.48, or about 7.5 hours later than Nakano's prediction.
  • APPARITION OF 2012
    [Perihelion Date=2012 October 1.97; Period=6.90 years]
  • Using positions from the 1998 and 2005 apparitions, S. Nakano, K. Kinoshita, and others predicted the comet would next arrive at perihelion on 2012 October 1.69. The first observations were acquired by H. Sato, who used the 51-cm astrograph and CCD camera at the remote observatory in Mayhill, New Mexico, USA on 2012 July 15, 16, 29, and 30. He gave the magnitude as 18.4 on the 15th, 18.2 on the 16th, 17.0 on the 29th, and 18.4 on the 30th.
  • With the maximum total magnitude expected to reach 15.1 during the latter half of 2012 September, it was certainly a surprise when Juan Jose Gonzalez-Suarez reported that a visual observation using a 20-cm reflector on September 6 revealed a total magnitude of 11.2 and a nuclear magnitude of 13.7. He added that the coma was very slightly condensed and 3.5 arcmin across. The outburst in brightness was quickly confirmed, with CCD images indicating a total magnitude near 13 and a nuclear magnitude near 14.5. Visual observers continued to reveal magnitudes between 11 and 12. A slow brightening continued for the next couple of weeks and then CCD images from various observatories indicated a further jump of 2 magnitudes in brightness between on September 22 and 24. This brought the total magnitude to about 10 and the nuclear magnitude to about 11.5. Interestingly, T. Seki (Japan) noted that longer exposure CCD images revealed magnitudes of 9.3-9.5 on September 23, 8.0 on the 25th, and 8.5 on the 26th.
  • Additional Images

    A. Nakamura photo of 168P exposed on 1999 January 13
    Copyright © 1999 by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan)

    The CCD image was taken on 1999 January 13.45, using a 0.60-m f/6 Ritchey-Chretien telescope. Three images were added to better reveal the comet. Subsequently every star appears three times.


    M.-T. Hui image of 168P exposed on 2012 September 10
    Copyright © 2012 by Man-To Hui (Xingming Observatory, Mt. Nanshan, China)

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