An asteroidal object of magnitude 18 was first discovered on Mar. 31, 2008 in the course of the Mt.Lemmon Survey and then again on July 1, 2008 in the course of the Siding Spring Survey. Detailled observations showed it to be of cometary nature. Comet C/2008 FK75 (Lemmon-Siding Spring) showed a 6" diffuse coma. It will pass its far perihelion in fall 2010 and could then reach magnitude 15, passing through the constellations Hercules, Lyra and Cygnus (IAUC 8958). The small number of published observations show that the comet peaked at about 14.5 mag in summer 2010. At this time the medium condensed coma showed a diameter of about 0.5'.
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An asteroidal object of 19 mag was found by the Catalina project on July 27, 2009 near the border of the constellations Aquarius/Capricornus. Detailed observations revealed the cometary nature. Comet C/2009 O2 (Catalina) will pass its perihelion in March 2010, expected to reach magnitude 9 (IAUC 9057). Mid-European observers can observe the comet from mid-January until the end of April. At magnitude 14 at first, it will peak in brightness just in time it reaches greatest altitude (30°). It will disappear under the horizon at the end of April, expected to be of magnitude 12. During this period it will move from Aquila through Cygnus, Andromeda, Taurus into Orion. A morning object at first, it will enter the evening sky in mid-March. It came as no surprise that the comet did not survive its perihelion passage. The value H10 = 11.0 mag for this comet is very close to the critical value set by the Bortle formula Hkrit = 7.0 + 6×q for comets which most probably will not survive their perihelion. Due to the very few estimates published until the start of April 2010 it is not possible to make even a crude analysis. The published observations only indicate that the comet reached magnitude 10.0-10.5 in the days around perihelion (Mar. 24). After that date visual observations ended. With large instruments the morphological changes were documented: while observations on Mar. 5 still showed a central condensation, this was no longer detectable on CCD images on Mar. 8, which did show a fan-shaped 1.5' tail in p.a. 300°. On images taken on Mar. 12 the coma showed as a very diffuse object with a 3x5' coma without any central codensation. On Mar. 14 the coma had faded about 1 mag in the R-band (IAUC 9131). Michael Jäger detected the comet as an extremely diffuse 15 mag object on images taken on Mar. 29. CCD-observations between Apr. 2 and 6 show a highly elliptical, extremely diffuse coma without any central condensation, estimated to be of magnitude 14-17 (MPEC 2010-G63, Comet's Mailing List).
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On Oct. 21, 2009 R.E. Hill dicovered a 17.5 mag comet with the 0.5m-Catalina-telescope in the constellation Taurus. Comet C/2009 U3 (Hill) showed a 15" coma with a 6" central region, elongated SW-NE, and a 20" tail in p.a. 220-230°. Observations with a 2m-telescope on Oct. 22 showed a 5.0x1.5" central region with the major axis in p.a. 75...255°. The comet will reach perihelion in March 2010, expected to reach magnitude 15 (IAUC 9086 / MPEC 2009-V58). During the most interesting weeks it will move from Andromeda through Cassiopeia into Camelopardalis. In spring 2010 the comet was surprisingly bright. The few published observations give a magnitude of about 13.5 between March and mid-April. Die medium-condensed (DC 3) coma showed a diameter short of 1'. Then the amateur observations end; the last published observation (beginning of June) lists the nuclear magnitude as 19.5 mag, indicating a total magnitude of about 17.5 mag. Thus the comet has experienced an outburst, which ended during the second half of April.
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An apparently asteroidal object of 19.5 mag, discovered by the Catalina team on Dec. 17, 2009 near the border of the constellations Canes Venatici / Ursa Major revealed its cometary nature during follow-up observations. Comet C/2009 Y1 (Catalina) showed a faint tail in p.a. 260° and weak activity west of the nucleus. It will reach perihelion at the beginning of 2011, expected to reach 15 mag (IAUC 9102 / MPEC 2010-C27).
The comet was 2 mag brighter than expected (13.0 mag) in fall 2010, according to international observations. However, they also hint to an activity significantly below average. The coma diameter was estimated short of 1'. In summer 2011 the comet was still of magnitude 13.5, showing a 1' coma, which was not much condensed (DC 3).
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On Jan. 6, 2010 the LINEAR team discovered an asteroidal object of 20 mag in the constellation Gemini, which revealed its cometary nature on detailled observations on Jan. 7.0 UT. Comet P/2010 A2 (LINEAR) was a headless object of total magnitude 18.5 with a straight tail in east-western direction (p.a. 280°). The tail was 130" long, with a constant width of 10-14" along its entire length. Starting 6" from the eastern end it was brightest in an 20" area, however not showing any obvious central condensation. The tail faded gradually towards west. On Jan. 7.7 UT a faint 0.5' coma and a 5' tail was observed. This comet is the 5th member of the Main Belt Comets, being situated in the inner part. The comet passed perihelion on its orbit with a period of only 3.5 years in November 2009, peaking at the time of discovery. Observations on Jan. 11 show a stellar nucleus of magnitude 23 (estimated diameter: 150-200 m) 2.5" in front of the dust tail, connected with it via a light bridge. The most probable explanation of this unusual object is a collision between two small asteroids (IAUC 9105/09/10, CBET 2134).
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An asteroidal object of magnitude 17.5, discovered by R.D. Cardinal on Jan. 19, 2010 near the border of the constellations Camelopardalis/Ursa Major revealed its cometary nature on subsequent observations. Comet C/2010 B1 (Cardinal) showed a softer image than the surrounding field stars. The diameter of the strongly condensed coma was measured to be 7". The comet will pass perihelion in February 2011, expected to reach magnitude 14 (IAUC 9113). It should be brighter than 16.0 mag between September 2010 and September 2011. Mid-European observers can follow the comet until mid-March 2011. During this period it will move from Gemini through Canis Minor, Monoceros, Orion into Eridanus, when it will disappear above the southwestern horizon. The comet peaked at 13.5 mag in winter 2010/11, showing a coma of about 1' diameter.
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On Mar. 23, 2010 Don Machholz visually discovered - after he had searched for 607 hours - a comet with his 47cm-reflector in the northern parts of Pegasus. Comet C/2010 F4 (Machholz) showed a diffuse 2' coma (DC 2) of magnitude 11.5. He could not detect any motion on this date, due to encroaching twilight. Machholz found the comet again of similar appearance on the morning of Mar. 26, indicating that it is moving rapidly towards the sun. Additional observations indicated a perihelion date of Apr. 6, when the comet reached a distance of 0.6 AU to the sun. However, due to its inherent faintness, the comet was not expected to become brighter than about 11 mag (IAUC 9132 / MPEC 2010-G43). Mid-European observers could only glimpse the comet in the days before perihelion above the northeastern morning horizon. The very few published observations indicate a maximum brightness of 10.5-11.0 mag. The diameter of the medium-condensed (DC 3) coma was in the order of 1.5-2'.
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On images taken in the course of the Catalina Sky Survey on Apr. 5, 2010 A. Boattini disovered a 14.0 mag comet in Taurus. Comet C/2010 G1 (Boattini) showed a strongly condensed 40" inner coma, surrounded by a diffuse outer coma up to 2' in diameter. The comet passed perihelion a few days prior to discovery and was expected to fade rather rapidly thereafter (IAUC 9133). It could be observed from mid-European locations until the start of May, when it would have moved into Orion. During the second week of April the very few published observations report a magnitude of about 13.5. The diamater of the medium-condensed (DC 3) coma was estimated to be 0.8'.
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The apparition 2010 of comet 2P/Encke (P=3.30a) could only be followed from the southern hemisphere. The first observations date of Aug. 17, with the comet estimated at 7.5 mag, showing a 3' (160.000 km) coma. In mid-September the comet had faded to 10.5 mag, showing a coma diameter of 2' (100.000 km). The brightness evolution can be well represented by the formula m = 3.6 mag + 5×log D + 6.7×, which is typical for this comet.
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Comet 65P/Gunn (P=6.79a) was observed visually at about magnitude 13.5 already at the beginning of 2009, about one year prior to perihelion. Thus this comet should reach magnitude 12 during summer 2010. However, it will then be positioned in the southernmost corner of Capricornus, being a very diffucult object for mid-European observers. The comet displayed a very steady brightness evolution, which can be well simulated by the formula m = 6.2m + 5×log D + 11×log r. The maximum brightness of 11.7 mag was reached in mid-July 2010. Due to the relatively small variance in the solar distance the parameters can not be established with the usual accuracy. In 2009 the coma diameter was short of 1.0' (100.000 km), in 2010 measured a bit more than 1.0' (90.000 km). The differences in the apparent and absolute coma diameters are a result of the smaller distance to Earth in 2010, which may also be the reason for the coma degree of condensation estimated at DC 5 in 2009, but only DC 3-4 in 2010.
Total Brightness and Coma Diameter
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According to a handful of observations comet 240P/NEAT (P=7.59a) peaked at magnitude 14.5 mag in December 2010 - 1.5 mag brighter than predicted. The considerably condensed coma exhibited a diameter of only 0.4'. Additional CCD-observations during the following months indicated a significantly slower fading than expected. Surprisingly at the end of May it was again estimated at 15.0 mag - 4 mag brighter than expected. The significantly condensed (DC 6) coma was of diameter 0.7'. In addition observations by Bernd Häusler show an outburst of magnitude 2-2.5m at that time.
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On images of Dec. 11, 2010 the asteroid (596) Scheila showed cometary structures. The 13.4 mag coma showed an envelope that extended 2' towards north and 5' to the west. On images of Oct. 18 and Nov. 11 the asteroid showed a stellar appearance at magnitude 14.5. Then on Dec. 3 the asteroid showed some slight diffuseness at magnitude 13.2 (IAUC 9188). Observations in 2006 indicate a brightness variation typical for an asteroid with H=8.84 mag / G=0.076 and an amplitude of 0.09 mag. In November 2010 the absolute brightness was already 0.1 mag brighter than expected. In Dezember, when the coma was obvious, the asteroid was about 1 mag brighter than the above parameters indicate (CBET 2590). Spectroscopic observations in mid-Dezember 2010 and during the first days of January 2011 show no gasous components within the coma. VLT-observations on Dec. 12 show a 1' structure, which originated in the northeastern part of the coma and then curved toward the anti-solar direction. A second structure was 30" long, originating in the south and curving towards p.a. 230°. In addition a narrow 45" tail could be detected. On Dec. 21 both structures had grown fainter and larger (4' and 2'). On Jan. 4, 2011 both were even fainter and larger (7' and 4'). This evolution do not hint to a continuous activity but to a singular event, most probably a collision (CBET 2632). The number of observations I could collect from this object is surprisingly small, the following conclusions accordingly uncertain. Visual observers reported a maximum brightness of 11.7 mag (2.5 mag brighter than normally) and a maximum coma of 3.5'. Only three weeks later, in the first days of January, the minor planet appeared star-like for visual observers. However, the reported magnitude was still about half an magnitude brighter than normally. Eventually, since the beginning of March visual observations show a star-like object at the expected magnitude. Thus it is most probable that the minor planet experienced an impact.
Andreas Kammerer
