C/2001 A2 (LINEAR)

This comet was discovered by the LINEAR telescope on January 15th 2001 at magnitude 19 and confirmed to be cometary by Petre Pravic at Ondrejov. On investigation, it was found that the comet had previously been observed by LINEAR on January 3rd, 5th and 6th - a total of 17 pre-discovery observations. However, the comet had been first observed by LONEOS, which obtained 4 images on January 3rd, two of them before the first LINEAR image, the first of them 47 minutes before LINEAR's first image.

It was found that C/2001 A2 (LINEAR) was only 4 months from perihelion and would be only just outside the orbit of Venus at the time. Being so faint though its absolute magnitude was only 13.5, 7 magnitudes fainter than the "average" new comet, so it was not expected to get brighter than magnitude 10 at maximum. That it did was due to a series of huge outbursts that increased its brightness by a factor of almost 3 orders of magnitude.

Many of the outbursts were associated with the observation of secondary fragaments. This provides strong support for the rubble-pile model of the nucleus where small fragments separate from the main nucleus and evaporate or lose their volatiles very rapidly.

Planetary perturbations are progresively closing the orbit which has a semi-major axis a little under 1000AU. Perihelion was passed at 12:29UT on May 24th 2001 at 0.779AU. The orbit has an inclination of 36.5 degrees.

The light curve

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The light curve is well covered. There are 277 observations, made up of 88 total visual magnitude estimates and 189 CCD estimates that cover the period from April 1st 2001 to September 28th 2002.

Note the very rapid rise and fall of the light curve. The comet passed from magnitude 3.5 on June 22nd (Francisco Rodríguez), to 10.0 on August 8th (Paco Reyes).

The last observation recorded by the Minor Planet Center put the comet at 16.5 on 2001 Nov. 18th. However, on 2002 Sep. 15th Ramón Naves and Montse Campàs recorded a very faint image of the comet at magnitude 19 from their backyard observatory. The position and motion of the comet agree with the calculated ephemeris, although it was somewhat brighter than expected. This observation came after a series of failures and suggests that there may have been a further outburst at r=6.0AU. On 2002 Sept. 28.0 three images of the comet were also recorded at Teide Observatory, by Fabiola Martín-Luis with the 82-cm IAC-80 Telescope with an R filter, through moderate cirrus cloud. The images are very faint and were measured with a 2.2 arcsecond aperture to minimise the sky background. Although slightly fainter, the position and total magnitude are consistent with the data from Ramón Naves and Montse Campàs.

 

 

 

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When we examine the light curve separated by observers we see that there are excellent sequences of total visual magnitude data by Paco Reyes and Giovanni Sostero. Francisco Rodríguez covers the maximum of the light curve in late June.

Many other observers contribute a small number of observations.

 

 

 

 

 

 

 

 

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The light curve behaviour with heliocentric distance is very interesting. Here the two relationships (for the total visual magnitude and for CCD data) are shown. Note the very rapid rate of visual deline which goes as a 6th power law.

The CCD data shows a larger dispersion. Part of this is due to the fact that a few points were taken with an aperture larger than the standard 10 arcseconds. Some of it though is real variability. The September 15 th 2002 point is a somewhat brighter than expected from the extrapolation of the 2001 data, supporting suggestions that it may represent a significant new outburst that permitted its detection. The Teide Observatory point from September 28th lies closer to the extrapolation of the line of CCD magnitude, although not too mucho should be read into the photometric precision of this point.

The brightening law for the CCD data is significantly flatter than for the visual data. This is largely to be expected as close to perihelion and perigee the fraction of the coma enclosed by the 10 arcsecond aperture is much smaller than at larger distances, thus making the comet seem artificially faint.

 

 

 

Observations by:

  • Ramón Naves & Montse Campàs - MPC 213
  • Albert Sánchez - MPC 442
  • Salvador Sánchez & Juan Rodríguez - MPC 620
  • Fabiola Martín-Luis - MPC 954
  • Giovanni Sostero & Luca Donato

 Visual data by:

  • Javier Bros
  • Neilia Campos
  • Emili Capella
  • Valentín Díaz
  • Silvia Díaz Smith
  • Federico Fernández
  • Faustino García
  • Pedro Girona
  • Francisco González
  • Oswaldo González
  • Paco Ocaña
  • Paco Reyes
  • Marisol Riquelme
  • Albert Sánchez
  • Giovanni Sostero