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Interesting Fainter Comets 2012


An asteroidal object of magnitude 18.5, discovered on Sep. 21, 2010 by the LINEAR team in the constellation Camelopardalis revealed its cometary nature on subsequent observations. Comet C/2010 S1 (LINEAR) showed a miniscule coma of total magnitude 17.5 - which was only marginally larger than the images of the adjacent stars - and a short tail. The inherently bright comet will pass perihelion in May 2013 and could then peak at magnitude 14-15 (IAUC 9170 / MPEC 2010-U55). During the most interesting months it will move through the constellations Cygnus, Vulpecula and Sagitta, thus being well-placed for mid-European observers with large instruments.
The evolution of this comet can be derived from 43 observations by 5 members of the German Comet Section and 140 international observations, spanning more than 3 years of coverage (July 2011 to Sep. 2014). These indicate an extremely slow brightness evolution, best described by time-dependent parameters, distinguishing the periods prior and past perihelion. Pre-perihelion the parameters are m0=9.3 mag / nt=0.0005, post-perihelion m0=9.3 mag / nt=0.0010, yielding the following maxima: Nov./Dez. 2011: 13.6 mag, Sep. 2012: 13.2 mag, Aug. 2013: 12.9 mag, July 2014: 13.4 mag.
The comet shows a miniscule coma, fluctuating between 0.6' and 0.8' in accordance to the changing distance to earth. This implies a rather constant coma diameter between 225.000 km and 250.000 km during the whole apparition. The degree of condensation declined continuously during the apparition, measuring DC 6 in 2011, but only DC 3-4 in 2014. Visual sightings of the tail (not exceeding 2') required large instruments and have only been reported during summer/fall 2013.

Total Brightness and Coma Diameter

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R.H. McNaught discovered a further comet with the 0.5m-Uppsala-telescope on Sep. 3, 2011 in the constellation Fornax. Comet C/2011 R1 (McNaught) showed a round, 12" coma of magnitude 16.5 and a hint of a 0.2' tail, pointing towards Northwest. It will pass perihelion in October 2012, expected to reach 12 mag (IAUC 9230 / MPEC 2011-R35). However, at this time it will be positioned in the far-southern sky. Mid-European observers could try to get a glimpse of this comet until mid-January 2012 in the midnight/evening sky, with the comet at altitudes below 10°. More promising will be the second apparition, starting in March 2013 in the morning sky. At about 12.5 mag it will be situated in Scorpius. The fading comet should reach 16 mag in August 2012, being then situated in Virgo.
Until January 2013 the comet could only be observed from the Southern hemisphere. The 3 observations by 2 members of the German Comet Section and the 45 international observations indicate a low activity. The brightness evolution can be represented quite well by the parameters m0=8.2 mag / n=2, which indicate a maximum of 11.5 mag in mid-August 2012. The comet should have reached a secondary maximum around 11.9 mag at the end of March 2013, but this is not well documented. Surprisingly, the coma diameter decreased from 2.5' (290.000 km) to 1.5' (160.000 km) during the apparition, the degree of condensation from DC 3 to DC 1-2. This could indicate that the activity diminished continuously.

Total Brightness and Coma Diameter

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An asteroidal object of magnitude 18.5, discovered by the LINEAR-project near the border of the constellations Hercules/Ophiuchus on Oct. 31, 2011 accidentially got an asteroidal designation, although H. Sato had already reported a diffuse coma. According to H. Sato comet C/2011 UF305 (LINEAR) showed a 20" coma of magnitude 17.5 and a 9" tail towards p.a. 99°. The comet will pass its perihelion in mid-July 2012 and could be as bright as 14.5 mag for a couple of weeks. Thereby it will pass the North Pole at a distance of only 5° (CBET 2960). It should be brighter than magnitude 16.0 between March 2012 and January 2013, moving through the constellations Cepheus, Cassiopeia, Camelopardalis, Ursa Major, Ursa Minor, Leo Minor, Leo and Cancer into Canis Minor. Thus it will be a circumpolar object for about half an year, as observed from latitudes north of 45°N.
Only 4 observations by 3 members of the German Comet Section and 35 international observations came to my knowledge. The brightness evolution can be described with the formula m = 3.0 mag + 5×log D + 20×log r, yielding a maximum brightness of 11.8 mag at the end of June 2012. The coma diameter increased from 0.6' (75.000 km) at the start of the apparition to 1.8' (225.000 km) in June 2012. Thereafter it decreased, reaching 1.1' (110.000 km) at the end of November. The degree of condensation decreased from DC 6 at the beginning of the apparition to DC 2 in September. At the end of the apparition it was estimated to be DC 1-2.

Total Brightness and Coma Diameter

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An asteroidal object, discovered by the LINEAR project on Jan. 15, 2012 in the constellation Canes Venatici revealed its cometary nature at closer inspection. Comet C/2012 A2 (LINEAR) showed a diffuse 15" coma of magnitude 18.0, that displayed a moderately condensed central condensation. In addition a faint 20" tail in p.a. 240° could be discerned. The comet will pass perihelion in November 2012, expected to reach magnitude 16.5. It will pass the Northern Pole at a distance of only 2° around this date (CBET 2977 / MPEC 2012-C24).
According to the small number of observations (which scatter significantly) this comet was about 3.5 mag brighter than expected during summer 2012 (about 13.5 mag). Thereafter the comet faded despite the further decreasing solar distance. This indicates a fading absolute magnitude caused by a decrease of the activity level. According to the CBAT pages the comet was estimated to be only 16.5-17.0 mag at the end of March 2013. The very small number of observations hints to a constant level of activity prior to perihelion (m0=10.5 mag / n=0) and a rapid decline post-perihelion (m0=10.5 mag / nt=0.015). The diameter of the moderately condensed coma was estimated to be less than 1'.

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On Feb. 11, 2012 the American amateur Manfred Bruenjes discovered a comet of magnitude 15, showing a 1' coma on his CCD-images, taken with a 36cm-Schmidt-Cassegrain-telescope in the constellation Aries. Additional observations of comet C/2012 C2 (Bruenjes) showed an extremely diffuse coma of up to 7' and magnitude 10.5-11.0. The comet passed perihelion in mid-March, after approaching Earth to within 0.20 AU on Jan. 27. Based on the discovery brightness it should have peaked at magnitude 9.0 at perigee, being brighter than 10.0 mag between Jan. 23 and Feb. 2. Thus it is surprising that it was not discovered earlier. However, near perigee it would have shown a diameter of double size, thereby passing the Milky Way. Thus it is not necessary to assume an outburst to explain the late discovery. Although the comet still approaches the Sun, its distance to Earth is already increasing, resulting in a fading of the object. At the time it will disappear above the mid-European western evening horizon its brightness is expected to be about magnitude 12.
Only a small number of published observations of this comet could I recognize, covering only 8 days (Feb. 15 - 23). Due to the rather large coma the estimates scatter considerably, preventing any definite conclusion about the brightness parameters. However, the estimates are compliant with the values m0=12.0 mag/n=4, yielding a constant brightness of about 11.5 mag throughout the 8 days. The coma was estimated to be 3' (roughly 100.000 km), with a degree of condensation of about DC 2.

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On Feb. 5, 2012 an asteroidal object of magnitude 18 was discovered in Leo in the course of the Morocco Oukaimeden Sky Survey (MOSS). Further observations showed the object to be cometary. Comet C/2012 CH17 (MOSS) showed a strongly condensed, 15" coma and a 20" tail towards p.a. 264°. It will pass perihelion at the end of September 2012 and could reach magnitude 13.5 (CBET 3020). However, it will be a very difficult object for mid-European observers, reaching altitudes of less than 20° from July onward (then at magnitude 15.0).
Only a very small number of observations has been published, which scatter significantly. According to these the comet seems to have reached a maximum of 14-15 mag in August 2012. The coma diameter was estimated at less than 0.5'. In Comet's Mailing List Seiichi Yoshida pointed to the fact that the comet grew ever more diffuse during the whole apparition.

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An asteroidal object, discovered by A.R. Gibbs on images taken on May 13, 2012 in the course of the Catalina Sky Survey in the constellation Pegasus showed its cometary nature in follow-up observations. Comet C/2012 J1 (Catalina) showed a 10" coma of total magnitude 17.0 and a faint 16" tail in p.a. 210°. It will pass perihelion in December 2012 and could reach magnitude 15.0 in fall (CBET 3104 / MPEC 2012-L43).
Based on 3 observations by 3 members of the German Comet Section and 40 international observations no definite results can be derived. The brightness evolution is best described by the parameters m0=10.8m / nt=0.008. According to these the comet reached a maximum of 12.8 mag at perihelion. During the apparition the apparent coma diameter increased continuously from 0.5' (60.000 km) to 1.3' (150.000 km) in December 2012. Thereby the coma was always significantly condensed (DC 5-6).

Total Brightness and Coma Diameter

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On June 1, 2012 the LINEAR project discovered a 19.0 mag object in the constellation Draco, which proved to be a comet. Comet C/2012 L1 (LINEAR) showed a medium condensed 10" coma of total magnitude 18.5 and a 40" tail in p.a. 220°. It will pass perihelion on Christmas Eve and could reach magnitude 15.5 (CBET 3134 / MPEC 2012-L43). During the most interesting weeks (December/January) it will move from Ursa Minor towards Perseus, thus will be visible the whole night for mid-European observers. On Dec. 19 it will pass the North Pole at a distance of only 1°. According to the most recent elements the comet orbits the sun about every 5.000 years.
Only one visual and a small number of photographic observations came to my knowledge. These indicate a maximum brightness of the small coma (short of 1') of about 14.0-14.5 mag.

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An asteroidal object discovered by the La Sagra project with a 0.45 m telescope on July 13, 2012 near the border of the constellations Pegasus/Pisces showed its cometary nature on deep images taken with the 1.23 m telescope at Calar Alto. Comet P/2012 NJ (La Sagra) was of magnitude 14.5, showing a 35" tail in p.a. 235°. It passed perihelion on its 24.8 years orbit, which is almost perpendicular to the ecliptic, in mid-June. However, because it still approached Earth (minimum distance of 0.582 AU occurred on July 22), it still brightened during the following 4 weeks (CBET 3178 / MPEC 2012-R16).
Visually the comet appeared totally stellar. The few observers following this unusual object reported a maximum brightness of 14.0 mag in the days of perigee. The brightness parameters can only temporarily derived to be about m0=14.5 mag / n=2, i.e. the comet behaved like a reflective body, which is no surprise keeping in mind the stellar appearance. The short tail could only be recorded photographically.

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According to the rather small number of published observations comet 185P/Petriew (P=5.46a) showed a similar rapid evolution during its apparition of 2012 than in 2001. Short after perihelion (at the end of August) it reached a maximum of 10.0 mag. The brightness evolution can be well described by the parameters m0=10.5 mag / n=12. The diameter of the diffuse coma (DC 3) reached a maximum of 3'.

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Much brighter than predicted was comet 246P/NEAT (P=8.08a) in spring 2012. The total of 35 visual observations show too large a scatter to analyze them properly. Most plausible are the brightness parameters m0=6.0 mag / n=4, which would indicate a maximum brightness of 13.0 mag in spring 2013. The coma diameter is estimated to be about 0.7' (75.000 km). Similarly the estimates of the degree of condensation also scatter widely, concentrating on values between DC 4 and DC 5.

Andreas Kammerer


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