C/2002 T7 (LINEAR)

Orbit and Ephemeris by Central Bureau for Astronomical Telegrams

M. Jäger and G. Rheman photograph of C/2002 T7 on 2004 May 22

This image was obtained by M. Jäger and G. Rheman on 2004 May 22.77. It was obtained with a 50mm Nikon lens and a Starlight SXV-H9 CCD camera. The bright star near the top of the image is Sirius, while the cluster to the left of the comet is M41.

Discovery

The LINEAR project announced the discovery of an asteroidal object on images obtained on 2002 October 14.42. The magnitude was given as 17.5. Several observatories obtained follow-up observations as October progressed. Interestingly, P. Birtwhistle (Great Shefford, U.K.) noted that CCD images obtained with a 0.3-m Schmidt-Cassegrain on October 28.0 revealed the comet appeared "softer" than nearby stars of similar brightness. T. B. Spahr (Whipple Observatory, Mt. Hopkins) obtained CCD images with a 1.2-m reflector on October 29.4 and noted the object appeared "very slightly diffuse" with a total magnitude of 17. IAU Circular No. 8003 (2002 October 29) announced this object was really a comet. Prediscovery observations were found on LINEAR images obtained on October 12.

Historical Highlights

The first published orbit came on 2002 October 29. B. G. Marsden (Central Bureau for Astronomical Telegrams) took 88 positions spanning the period of October 12 to 29, and calculated a parabolic orbit with a perihelion date of 2004 April 23.69. Ultimately, the comet proved to be moving in a hyperbolic orbit, with a perihelion date of April 23.08.

The comet slowly brightened during 2003, although the pace quickened during the last couple of months of the year. Magnitude estimates were near 14 during February and March, and finally reached 13 at the end of August. More and more observers began following the comet starting in October, when the comet surpassed magnitude 12. As the year came to a close the brightness had nearly reached magnitude 8, while the coma was typically estimated as between 4 and 6 arc minutes.

As of mid February 2004, several observers have independently noted the comet has not increased in brightness as rapidly as predicted during the last month, including myself. Through the first half of February the comet has shown very little change from a magnitude of 7. It is too soon to know all of the possible ramifications of this, but the rate of brightening has decreased. German amateur astronomer Maik Meyer suspects the comet may be dropping back to the rate of brightening it experienced prior to the sudden change last October. If so, this will seriously affect the predictions--and not in a favorable direction.

The comet was observed in twilight during the first week or so of March and several observers noted a magnitude slightly brighter than 7. Observations seemed to have ceased on March 10, as the comet was too deep in twilight. The comet passed about 9° from the sun during late March. The first observation following conjunction with the sun appears to have been made on April 9, when Alexandre Amorim (Florianopolis, Brazil) saw it in bright twilight using 20x80 binoculars, with Andrew Pearce (Kalgoorlie, W. Australia) also spotting it with 20x80 binoculars a few hours later. He gave the magnitude as 4.6 and said the coma was 6 arc minutes across.

Although the comet passed perihelion on April 23, it passed 0.27 AU from Earth on May 19, which caused it to slowly brighten through most of May. The magnitude was about 4 as May began and appears to have peaked between magnitude 2.5 and 3.0 during the period of May 20 to May 25. At its peak, the comet was at a low altitude for Southern Hemisphere observers and the coma was generally estimated as 10 arc minutes across. The first Northern Hemisphere observer was Francisco A. Rodriguez Ramirez (Gran Canaria - Canary Islands) on May 25, when he noted it was "clearly visible to the naked eye." The next Northern Hemisphere observation came from Mike Linnolt (Honolulu, Hawaii), who spotted it with 10x50 binoculars on May 27.

This comet surprised a lot of people shortly after mid-May. First, the brightness curve was not smooth, but contained several unexplained dips and rises, which indicate the comet was fluctuating in brightness. Second, where most observers were reporting a tail length of 1° to 2°, there were indications of a much longer tail. Andrew Pearce (Noble Falls, W. Australia) had consistently reported a tail length of 4° to over 6° since the latter half of April and David Seargent (Cowra, New South Wales, Australia) was able to follow the tail for 13° with 2.5x25 binoculars on May 19.35. Most interesting was the photograph by John Drummond (Gisborne, New Zealand) that he had photographed a tail 43° long with a 24mm lens on May 19.30. Drummond's fellow New Zealander, Ian Cooper, obtained several images from the 16th to the 22nd, which showed a dramatic increase in the tail length to the 19th and then a rapid decline. Although the report of these images initially generated some controversy, Terry Lovejoy immediately offered confirmation when he displayed an image he took on May 20 that showed the tail extending out of the field of his camera, which indicated a tail length of over 25°. Lovejoy further pointed out that at the time of Drummond's observation the "end section of the ion tail ... was problably <0.1 AU from the earth."

Additional Images

R. Ligustri and V. Savani photograph of C/2002 T7 on 2003 November 28

G. Masi and F. Mallia photograph of C/2002 T7 on 2003 November 29

This image was obtained by G. Masi and F. Mallia using a 0.81-m, f/7 telescope and a CCD camera on 2003 November 29.25. It is a combination of three 1-minute exposures. The B&W image was log scaled; on the right: the upper image shows the application of the Larson-Sekanina gradient to better investigate the activity in the inner coma, while the bottom panel shows isophotes, calculated on the log-scaled image.

L. Møller and M. Winther photograph of C/2002 T7 on 2003 December 11

This image was obtained by L. Møller and M. Winther using a 16-inch, F/10 SCT and an Apogee AP 6E CCD camera on 2003 December 11.85. This is a 200-second CCD image.

M. Jäger and G. Rheman photograph of C/2002 T7 on 2003 December 20

This image was obtained by M. Jäger and G. Rheman using a 250/450 Schmidt camera and an SXV-H9 CCD camera on 2003 December 20.72. This is a composite of three 120-second exposures. The coma is more than 10 arc minutes across, while the tail extends 15-20 arc minutes toward PA 90°.

Photograph of C/2002 T7 on 2003 December 28

This image was obtained by high school students using a 16-inch, F/10 SCT and an Apogee AP 6E CCD camera on 2003 December 28. This is a 420-second CCD image.

Dennis Persyk photograph of C/2002 T7 on 2004 January 13

This image was obtained by Dennis Persyk using an NP101 4-inch refractor and an MX716 CCD camera on 2004 January 13.03. This is a composite of fourteen 5-minute exposures. Although transparency was poor because of high cirrus clouds, the image reveals a tail 22 arc minutes long. North is up and east to the left. The image was reversed by the webmaster to better represent the comet's true appearance.

M. Jäger and G. Rheman photograph of C/2002 T7 on 2004 February 16

This image was obtained by M. Jäger and G. Rheman on 2004 February 16.75. It was obtained with a 20-cm Celestron Schmidt-Cassegrain and a Starlight SXV-H9 CCD. The bright star near the top of the image is Gamma Pegasi.

V. A. Buso, G. Mazalán and M. Ascheri photograph of C/2002 T7 on 2004 April 20

This image was obtained by Víctor Ángel Buso, Gustavo Mazalán and Mariano Ascheri on 2004 April 20.38. It was obtained with a 28-cm Schmidt-Cassegrain Telescope and a CCD camera.

V. A. Buso, G. Mazalán and M. Ascheri photograph of C/2002 T7 on 2004 April 27

This image was obtained by Víctor Ángel Buso, Gustavo Mazalán and Mariano Ascheri on 2004 April 27.35. It was obtained with a 28-cm Schmidt-Cassegrain Telescope and a CCD camera.

Gianluca Masi and Franco Mallia photograph of the tail structure of comet LINEAR on 2004 April 30

This image was obtained on 2004 April 30.39-30.42, while using the 35-cm SoTIE telescope in Las Campanas. This is a 7-frame mosaic covering about 1.4° of the tail.

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