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C/2011 L4 (PANSTARRS)

Image of comet PANSTARRS on 2013 March 19
Copyright © 2013 by Michael Jäger (Austria)

M. Jäger acquired this image on 2013 March 19.78 UT using a 180-mm Leica Apo refractor and a Sigma 6303 CCD camera. A total of five 120-second exposures were stacked to produce this image.

Discovery

The 1.8-m Pan-STARRS 1 Ritchey-Chretien telescope (Haleakala, Hawaii, USA) discovered this comet on four CCD images acquired during 2011 June 6.39-6.43. The magnitude was given as 19.4-19.6.

Several prediscovery images have been found. S. Larson (Mt. Lemmon Survey, Arizona, USA) reported that C/2011 L4 was located on four images acquired using the 154-cm reflector and a CCD camera during May 24.31-24.33. He gave the magnitude as 18.9-19.2. Hidetaka Sato (Tokyo, Japan) had acquired two images of periodic comet 174P on May 30 using his 25-cm reflector and a CCD camera. After the discovery of C/2011 L4, he noted it had passed rather close to 174P. Upon rechecking his images, he located the new comet glowing at magnitude 18.6-18.8. The comet had reached a maximum solar elongation of 176 degrees on May 27. Around mid-June, four additional images of the comet were located on images that had been acquired by Pan-STARRS 1 during May 21.43-21.48. The magnitude was given as 19.5-19.9.

Historical Highlights

  • The comet was discovered at a distance of nearly 7.9 AU from the sun, which astronomers realize can make the determination of the orbit kind of tricky for a few weeks. Fortunately, prediscovery images were quickly identified after the comet's initial discovery announcement. This enabled G. V. Williams to publish an orbit on 2011 June 8 (two days after the actual discovery) that was based on 34 positions spanning the period of 2011 May 24 to June 8. The result was a perihelion date of 2013 April 17.12. As additional positions became available, the orbit was updated...initially the only constant was that the comet would be passing perihelion in 2013. Williams published revised perihelion dates of February 5.89 on June 12, March 23.86 on June 17, March 26.36 on June 24, March 8.82 on July 2, and March 11.06 on July 8. But all of these orbits indicated an interesting aspect to this orbit. On the day of perihelion the comet would be located only 0.30 AU from the sun, which indicated the possibility of a bright comet.

  • The comet was widely observed during the remainder of June as observatories around the world rushed to acquire observations of this potentially interesting comet. Various-sized telescopes, different types of CCD cameras, and a variety of exposure times revealed the comet's nuclear magnitude as anything from 17.1 to 20.3, with an average of 18.9. The comet moved northward following its discovery and attained a declination of -16.4 degrees on July 11. It then turned southward. The comet slowly brightened during this period and was followed until 2011 October 16, after which it became lost in the sun's glare. The nuclear magnitude was then given as 17.7.

  • Having moved southward since mid-July 2011, the comet attained a declination of -25.9 degrees on 2012 May 28 and then began a northerly motion. It had exited the sun's glare and was picked up on 2012 January 13 by observers using the Siding Spring-Faulkes Telescope South (New South Wales, Australia) at which time the total magnitude was given as 16.3. The first visual observation by an amateur astronomer was made on March 28, when J. J. Gonzalez (Leon, Spain) saw the comet using his 20-cm reflector, giving the magnitude as 14.6 and the coma diameter as 0.3 arc minutes. Visual observers continued to follow the comet as it brightened to about magnitude 12 by the end of June, 11.5 by the end of July, and 11.0 by the end of August. Having moved northward since late May, the comet attained a declination of -24.9 degrees on 2012 August 4 and then began a southerly motion. The last observation before the comet entered the sun's glare was by A. Amorim (Florianopolis, Brazil). He saw the comet on 2012 October 7, using his 18-cm reflector and estimated the magnitude as 10.0.

  • The comet reached a minimum solar elongation of 12 degrees on 2012 November 27. One of the earliest images acquired as it was exiting twilight came from Rob Kaufman (Bright, Victoria, Australia) on December 18. The comet then appeared to be about magnitude 9.5. The first visual observation made after exiting twilight was by Amorim on December 24. He saw the comet using his 18-cm reflector when it was at an altitude of only 8.5 degrees. He estimated the magnitude as 8.1 and said the coma was 1 arc minute across. Terry Lovejoy (Australia) managed to acquire several CCD observations with his 20-cm reflector during the next few weeks, giving the magnitude as 9.0 on December 24, 8.6 on 2013 January 1, and 8.4 on January 6. During this same period he reported that the coma diameter increased from 1.1' to 2.1'. On January 7, Willian Souza (Sao Paulo, Brazil) saw the comet using his 10-cm refractor, reporting a magnitude of 8.0 and a coma 2' across. Amorim made several observations during the remainder of January. Using a 7-cm refractor, he generally reported that the comet brightened from 8.7 on the 12th to 7.1 by the 30th, with coma diameters generally 2-3 arc minutes. Chris Wyatt (Walcha, New South Wales, Australia) observed the comet using a 11x70 binoculars and reported that it brightened from 8.4 on the 8th to 6.5 by the 31st, while the coma diameter was between 3.9' and 6'.

  • The comet reached a maximum solar elongation of 35 degrees on 2013 February 2 and attained a southerly declination of -46 degrees on February 5, before turning northward.

  • The comet passed closest to Earth (1.10 AU) on 2013 March 5 and was closest to the Sun (0.30 AU) on March 10. It was finally spotted by observers in the Northern Hemisphere on the night of March 9/10. Mike Linnolt (Ocean View, Hawaii, USA) saw the comet using 7x35 binoculars on March 10.21, when it was 5 degrees above the horizon. He estimated the magnitude as -1.0, noting a coma 2 arc minutes across and a tail 0.25 degree long. J. J. Gonzalez (Llanfranc, Girona, Spain) saw the comet using 10x50 binoculars on March 10.77, and gave the magnitude as 1.4. He said the coma was 2.5 arc minutes across, while the tail was 0.3 degree long. The comet was then still visible to observers in the Southern Hemisphere. A magnitude estimate by Wyatt on March 10.38, using 7x50 binoculars, was -0.3, when the comet was only 1.3 degrees above the horizon. He also noted the coma was 2 arc minutes across, while the tail was 15 arc minutes long toward the east-southeast. The comet reached a minimum solar elongation of 15 degrees on March 11.

    • Upcoming Highlights

  • The comet will attained its most northerly declination of +85.2 degrees on 2013 May 28.

  • The comet will reach a maximum solar elongation of 79 degrees on 2013 July 2.

    • Additional Images

    Image of comet PANSTARRS on 2011 June 7
    Copyright © 2011 by G. Sostero and E. Guido(Italy)

    G. Sostero and E. Guido acquired this image on 2011 June 7 using a remote telescope at Tzec Maun Observatory (New Mexico, USA). The telescope was a 35-cm reflector with a CCD camera attached. A total of 14 three-minute exposures were combined for this image.

    Image of comet PANSTARRS on 2012 July 14 and August 9
    Copyright © 2012 by Leonid Elenin (Russia)

    Images of PANSTARRS acquired by Leonid Elenin on 2012 July 14 (left) and August 9 (right).

    Image of comet PANSTARRS on 2013 January 7
    Copyright © 2013 by Terry Lovejoy (Australia)

    This image of comet PANSTARRS was acquired by T. Lovejoy on 2013 January 7.75 while the comet was situated against the Milky Way. This image combines thirty-two 20-second exposures that were acquired using his HyperStar Celestron 8 and a QHY9 CCD camera.

    Image of comet PANSTARRS on 2013 March 11
    Copyright © 2013 by Giuseppe Pappa (Sicily, Italy)

    G. Pappa acquired this image on 2013 March 11.74 UT using a Canon 100D and a 300mm lens. The camera was set to ISO 200 and the exposure time was two seconds.

    Image of comet PANSTARRS on 2013 March 12
    Copyright © 2013 by James Champagne (Canyonlands National Park, Utah, USA)

    J. Champagne acquired this image on 2013 March 12 UT using a modified Canon XTi and a Tamron AF 75-300 lens set at 300mm and f/7.1. The exposure was 2.5 seconds at ISO 1600.

    Image of comet PANSTARRS on 2013 March 13
    Copyright © 2013 by Robert Lunsford (California, USA)

    R. Lunsford acquired this image on 2013 March 13 UT using a Canon Power Shot S2 IS. This was a two-second exposure showing the comet a few degrees to the left of a very young crescent moon.

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