C&MS: C/2001 Q4 (NEAT)

C/2001 Q4 (NEAT)

Wally Pacholka photograph of NEAT on 2004 May 8

This image was obtained by Wally Pacholka from Joshua Tree National Park on 2004 May 8 UT. It was obtained with a Fuji digital camera mounted on a Kenko mount. A 75mm lens was used at f/2.4 and exposed for 90 seconds at ISO 1600. Over 7° of tail was visible.

Discovery

Several observatories in the United States and elsewhere search the sky every clear, moonless night to look for asteroids which might eventually pose a threat to Earth; however, with such a systematic search of the sky come other interesting discoveries as well. S. H. Pravdo, E. F. Helin, and K. J. Lawrence (Jet Propulsion Laboratory) announced that the 1.2-m Schmidt telescope at Palomar Observatory (California, USA) had found a comet on 2001 August 24.40 in the course of the Near Earth Asteroid Tracking (NEAT) program. The comet was found on CCD images and the astronomers were able to confirm the discovery on August 26 and 27. The comet was described as a round nebulosity measuring about 8 arc seconds across. The total magnitude as given as 20.0. Confirmations also came from other observatories on August 27 and these indicated a brighter total magnitude. J. Ticha, M. Tichy, and P. Jelinek (Klet Observatory) gave the magnitude as 17.8, while P. J. Shelus (McDonald Observatory, Texas, USA) gave it as 17.3.

Historical Highlights

This comet was first announced on IAU Circular No. 7695 (2001 August 28), when Daniel W. E. Green gave the discovery details, as well as a "very uncertain" orbit by Brian G. Marsden. The orbit indicated the comet might pass perihelion on 2005 August 25, with the closest distance to the sun being just over 4 AU. The reason for the orbit's uncertainty was because the comet was moving very slowly due to its rather great distance from the sun. Marsden's orbit indicated the comet was probably over 11 AU from the sun when discovered. Kazuo Kinoshita published an orbit for this comet on his website on September 5. This orbit used 25 positions spanning the period of August 24 to 31 and indicated a perihelion date of 2004 May 23 and a perihelion distance of 0.99 AU. Such an orbit indicated a potentially bright apparition for this comet, but little excitement was generated as more observations were needed to firmly establish an orbit. Confirmation of Kinoshita's calculations came on September 10, when IAU Circular No. 7711 included new positions, as well as an orbit by Green which was based on 38 positions from the period of August 24 to September 10. This orbit indicated a perihelion date of 2004 May 26 and a perihelion distance of 1.00 AU. Green wrote that the perihelion date "is still uncertain by several weeks, but it appears that this comet may become an easy binocular (and possibly naked-eye) object in May-June 2004." As it turned out, the comet was discovered when 10.1 AU from the sun.

The comet slowly brightened during the remainder of 2001 and throughout 2002. As 2003 began, the comet was still fainter than magnitude 15, but it steadily brightened as the year progressed, reaching 14 near the end of May, 13 early in July, and 12 around mid-September. September of 2003 also marked the time that amateur astronomers in the Southern Hemisphere began supplying regular visual observations of this comet. The coma diameter was typically given as 0.6 to 1.2 arc minutes. CCD images by amateurs also began showing a short fan-shaped tail pointing northward in July. By late September, this tail extended about 0.8 arc minutes toward the northwest. As 2003 came to an end, the comet had become slightly brighter than magnitude 10, with a coma diameter of about 2 arc minutes. A faint, fan-shaped tail extended about 4 arc minutes toward the east.

Predictions: The comet should be at its brightest during the first half of May. The Central Bureau for Astronomical Telegrams predicts a maximum magnitude of 0.9, although their brightness parameters have not been updated in many months. Several experienced amateur astronomers are keeping close tabs on this comet. Andreas Kammerer (Germany) looked at all available observations obtained up to the end of November 2003, and suggests the comet's total magnitude may reach 2. Seiichi Yoshida (Japan) indicated during the last days of 2003 that the maximum brightness might reach 2.

The comet steadily brightened as the year progressed. Observers indicated the brightness attained magnitude 8 in mid-February, 7 in mid-March, 6 as April began and 5 shortly before mid-April. The coma grew in size during this same period, with estimates near 2 arc minutes at the beginning of February, 5 arc minutes around mid-March, 10 arc minutes as April began, and 15 arc minutes around mid-April.

The comet finally appeared to amateur astronomers of the Northern Hemisphere on the night of May 3/4. Numerous observers in the United States, from Texas, New Mexico, Arizona, southern California, and Hawaii, were able to spot the comet at a very low altitude just below the star Epsilon Canis Majoris. Most observers described the comet as appearing like a globular cluster between 7 and 10 arc minutes across, while a few noted a tail extension. Around this same time, observers in the Southern Hemisphere were giving the magnitude as between 3.2 and 3.6 on that date. The comet passed closest to Earth on May 6 and quickly attained a higher altitude for northern observers during the next week. Naked-eye observations were obtained from dark-sky locations and observers generally noted a magnitude of 2.8 to 3.0, while the coma diameter was generally estimated as 20 to 30 arc minutes. The tail was initially a short stub, but soon became longer and developed a filamentary structure. In addition, many observers noted the sunward side of the coma was abnormally bright, and many specially processed digital images revealed hoods near the nucleus.

This was another classic example of a comet exhibiting a large coma which caused widely varying magnitude estimates. During the period around mid-May, magnitude estimates varied by at least one magnitude among observers, with the average magnitude near 3.4. Some observers were then giving coma diameters between 25 and 30 arc minutes. The comet faded to magnitude 4 by May 18 and about 5 by May 26. The coma diameter on the last date was generally estimated as between 10 and 15 arc minutes.

Additional Images

Terry Lovejoy photograph of NEAT on 2003 August 26

Closeup of C/2001 Q4 on 2003 August 26.77 UT at 1.8 arc sec per pixel using a Tak E160. Image is 35 minutes exposure, with DDP processing and a slight median filter applied to clean up noise. Estimated magnitude was mag 11.9 (CCD USNO R mag) with west at top and south to right. The tail can be traced 7 arc minutes in PA 310°.

Gustavo Mazalan & Victor Buso photograph of NEAT on 2003 September 24

Image of C/2001 Q4 on 2003 September 24.22 UT. The image was obtained with a Celestron 11-inch SCT and a PICTOR 416XT CCD camera. Five 25-second exposures were combined for this image. The image measures 24 by 17 arc minutes. North is toward the top, while east is to the left.

Gianluca Masi and Franco Mallia photograph of the tail structure of comet NEAT on 2004 April 16

This image was obtained on 2004 April 16.99, while using the SoTIE telescope in Las Campanas. A set of images were collected to create a mosaic, covering about 0.7 deg. Each area was imaged using a total integration time of 3 minutes. Then the frames have been shifted taking the comet motion into account, in order to keep the higher detail. The tail of the comet is clearly visible; the object was at about 25 deg above the horizon. On the bottom right, the region close to the false nucleus shows clear dust shells.

Terry Lovejoy photograph of NEAT on 2004 April 24

This image was obtained by T. Lovejoy on 2004 April 24.40 UT. It is a composite of seventeen 90-second exposures obtained with and Canon EOS 300D attached to a Takahashi Epsilon E160. The camera setting was 400 ASA. The field is 2.5° wide.

Giovanni Sostero image of comet NEAT on 2004 May 10

Günter Kerschhuber image of NEAT on 2004 May 12

This image was obtained by G. Kerschhuber on 2004 May 13.91. It is a composite of sixty-five 40-second exposures obtained with a Pentacon 300mm and a Starlight SXV-H9.

Jerry Armstrong image of NEAT on 2004 May 12

This image showing detail within the inner coma was obtained by J. Armstrong on 2004 May 12.06. It is a 20-second exposure obtained with a Meade 14-inch LX200GPS Schmidt-Cassegrain Telescope and an SBIG ST-1001 CCD camera. North is up. The camera was on-loan from the Fernbank Science Center.

Rolando Ligustri image of NEAT on 2004 May 13

Anthony Arrigo image of NEAT near the Beehive Cluster on 2004 May 15

This image of comet NEAT near the Beehive Cluster (M44) was obtained by A. Arrigo on 2004 May 15. It is a composite of eight 30-second exposures obtained with a Sony DSC-F717 digital camera and 1.7x teleconverter. The camera was piggy backed on a 120mm f/5 refractor sitting on a Losmandy G11 mount.

C. V. Darias image of NEAT on 2004 May 15

This image was obtained by C. V. Darias on 2004 May 15.94. It is a 2.5-minute exposure using Fuji X-tra 400 film and a 20-cm Celestron Schmidt camera. The image shows the comet as it was moving past the open cluster M44 in Cancer.

J. A. Labrador image of NEAT on 2004 May 15

This image was obtained by J. A. Labrador on 2004 May 15.94. It is a 2-minute exposure using a Canon D60 digital SLR camera set at 400 ASA, with an 85mm f/1.2 lens. The image shows the comet as it was moving past the open cluster M44 in Cancer.

This image was obtained by J. Melka on 2004 May 16.11. Four 1-minute exposures were obtained using a Canon D60 digital SLR camera set at 400 ASA, with 12-inch f/4.1 Newtonian reflector. These images were subsequently stacked using Registax 2.0 Freeware.

G. V. Schiaparelli Astronomical Observatory image of NEAT on 2004 May 16

This image was obtained by L. Buzzi, M. Auteri, and A. Aletti on 2004 May 16.89. They were using a 14-inch Celestron Schmidt camera stopped down to 280mm. This 4-minute exposure was obtained with 400 ISO film.

A. C. Bares image of comet NEAT on 2004 May 19

This image was obtained by M. Moeller, L. Moeller and M. Winther on 2004 May 19.95. It is a composite of eleven 60-second exposures obtained with a Canon EOS D10 camera mounted at prime focus on a 1140mm refractor.

A. C. Bares image of comet NEAT on 2004 May 22

This image was obtained by A. C. Bares on 2004 May 22.88. It is a composite of four 60-second exposures obtained with an FSQ 106 and an SXV-H9 CCD camera.

Giovanni Sostero image of comet NEAT on 2004 May 24

This image was obtained by G. Sostero on 2004 May 24.0. It is a 300-second exposure obtained with a Canon EOS D300 camera and an Intes 15-cm Maksutov astrograph. The field of view measures 1° by 1.4°.

cometography.com