On Sep. 19, 2006 the LONEOS team discovered a comet of magnitude 19 near the borders of Pisces and Pegasus. Comet C/2006 S3 (LONEOS) presented a diffuse 10" coma, which was elongated towards east, but no tail. At discovery it was at a distance of 14 AU from the sun. The comet will pass perihelion (distance about 5 AU) not until spring 2012, when it could be as bright as 12 mag (IAUC 8752, MPEC 2006-T23). It is expected to be brighter than 14 mag between summer 2010 and fall 2013, thereby moving through Aquarius, Ophiuchus, Libra into Virgo. Four observations from 2 members of the German Comet Section and 125 international observations (spanning the period May 2011 to March 2015) can be used as data base for the analysis. With the constraint that the variance regarding the solar distance was small during this period, resulting in a rather large uncertainty for the brightness parameters, the observations indicate a very low activity of the comet. Pre-perihelion it can be best simulated by the parameter set m0=8.7 mag / n=1, whereas the values are m0=7.7 mag / n=1 post-perihelion. Actually, these values even indicate a continuously decreasing activity. Applying the parameter sets results in a maximum brightness of 12.6 mag in mid-2012. During the analysis it became obvious that a number of very bright estimates in 2013 is problematic. Because the absolute coma diameters belonging to them are significantly larger than 1 mio. km - which is not very plausible - I did not give them the same significance as the other estimates. The comet evolved as depicted until it was lost by visual and CCD observers in 2015! The coma diameter evolved as follows: in 2011 it increased from 1.0' (225.000 km) to 1.5' (350.000 km), in 2012 from 0.8' (125.000 km) to 2.3' (500.000 km) and in 2013 measured somewhere between 1.2' (325.000 km) and 3.5' (950.000 km). At the beginning of 2014 the observers estimated 1.0' (350.000 km). On average the coma diameter measured between 300.000 km and 400.000 km. In parallel to the decreasing activity the coma grew ever more diffuse. The estimates of the degree of condensation evolved as follows: 2011: DC 6 -> DC 3, 2012: DC 5 -> DC 2-3, 2013: DC 3, 2014: DC 2.
Total Brightness and Coma Diameter
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On Mar. 19, 2009 R.H. McNaught discovered an extremely condensed comet of magnitude 17 near the border of the constellations Libra/Scorpius. Comet C/2009 F4 (McNaught) appeared softer then the stars nearby and showed a 12" appandage towards west. This comet with a very high absolute magnitude will pass perihelion at the turn 2011/12 and could reach 14.5 mag, but will then be positioned at high southern declinations (IAUC 9032 / MPEC 2009-G40). The comet reached 13.5 mag during winter 2011/12, showing a coma diameter of less than 1'.
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An asteroidal object, discovered by the WISE satellite already on May 10, 2010 in the constellation Grus showed a cometary morphology at the beginning of August 2011. Comet P/2010 JC81 (WISE) showed a 12" coma of magnitude 14.5-15.0 and a 35" tail in p.a. 45° (IAUC 9224). At the start of August the comet had appeared in the morning sky, situated in Lynx, slowly fading during the next weeks on its way towards Ursa Major. It rounds the sun on an 23.2 year orbit and reached perihelion (then probably 13.5 mag bright) in April, but was then too near the sun. At the end of August and beginning of September a few visual observations were published. According to them the comet was of magnitude 13.5-14.0, showing a 0.7' coma of DC 4. Only a small number of observations came to my notice. These indicate that the comet peaked at about 13.5-14.0 mag in September 2011, showing a medium condensed (DC 4) coma of about 0.7' diameter.
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On Catalina-Schmidt-Telescope images of Jan. 15, 2011 A.R. Gibbs discovered a 18.5 mag comet near the border of the constellations Coma Berenices/Virgo/Bootes. Comet C/2011 A3 (Gibbs) showed an 8" coma with a central condensation and a faint 20" tail in p.a. 275° (IAUC 9193). The comet will pass perihelion in mid-December 2011, expected to reach magnitude 15. The comet orbits the sun with a period of about 6.000 years. Only 35 international observations could be used for the analysis. These show an unusual brightness evolution which may be described by the parameters m0=2.8 mag / nt=-0.054, which the comet followed until it disappeared in the twilight at a magnitude of 9.0 mag - 4.5 mag brighter than predicted. It is quite unlikely that the comet followed this evolution until its perihelion in mid-December, when it was too close to the sun for observation. The coma diameter remained smaller than 0.5' (40.000 km) for weeks, but started to increase in mid-July and was estimated at almost 8' (1 million km) at the end of the apparition. In parallel the degree of condensation decreased from DC 8 to DC 1.
Total Brightness and Coma Diameter
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On June 3, 2011 R.H. McNaught discovered a comet in the constellation Aquarius with the 0.5m-Uppsala-telescope at Siding Spring. Comet C/2011 L3 (McNaught) showed a 18" coma of magnitude 16.0 and a 0.7' tail in p.a. 240°. Additional observations even showed a 40" coma of total magnitude 15.0 and a 60" tail in p.a. 235°. The comet will pass perihelion at the beginning of August when it could peak at magnitude 14-15 (IAUC 9214). During summer 2011 it will move through Pegasus, Equuleus, Delphinus, Sagitta and Lyra, being visible the whole night through.
The comet got much brighter than expected, as is shown by 2 members of the German Comet Section and by 35 international observations. However it did not evolve according to the standards. Its brightness evolution can be described by the formula m = 12.3 mag + 5×log D + 0.035×|t-T|, resulting in a maximum brightness of 12.6 mag at perihelion. The apparent coma diameter remained constant at 1.5' throughout the apparition, yielding an increase of the absolute coma diameter from 65.000 km to 110.000 km. The coma was moderately condensed, with the degree of condensation decreasing from DC 4 to DC 3.
Total Brightness and Coma Diameter
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Vladimir Bezugly (Ukraine) and R.D. Matson (U.S.A.) independently noticed a possible comet on SOHO SWAN spacecraft ultraviolet images of Aug. 23. and 25 in the constellation Centaurus. On Sep. 4 R.H. McNaught und M. Mattiazzo succeeded in taking confirming images. Comet C/2011 Q4 (SWAN) presented a 3.0' coma of magnitude 11.5 (IAUC 9230). The comet passed perihelion on Sep. 20. Because it had approached earth within 0.66 AU at the start of August, it peaked at magnitude 11.0 already at that time. Due to its northward motion it will appear in the morning sky in mid-November for mid-European observers. Until the end of year it will move from the northeastern corner of the constellation Virgo into Bootes, passing Arcturus nearby.
The few published reports are inconsistent. They only marginally hint towards the brightness parameters m0=8.5 mag / n=6. The comet reached magnitude 9.5 during August, with the weakly condensed coma estimated between 2' and 3'. The orbital period of the comet was determined to be 290 years (MPEC 2011-S56).
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In summer 2011 comet 21P/Giacobini-Zinner (P=6.60a) was rediscovered. It will pass perihelion in February 2012, expected to peak at 10.5 mag. However, mid-European observers can follow it in the evening sky only until mid-January. The number of published observations is very small (covering the period mid-October 2011 to mid-February 2012), allowing only a very crude analysis. The brightness evolution can be described by the parameters m0=6.2m/n=9. The comet was of magnitude 14.5 in mid-October 2011, brightening to 8.0 mag until mid-January 2012, holding this brightness during the following 2-3 weeks. Due to the low altitudes the estimates of the weakly condensed (DC 3) coma scattered between 3' (125.000 km) and 5' (225.000 km) at the beginning of 2012.
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In spring 1984 comet 27P/Crommelin (P=27.92a) was one of the test comets for the International Halley Watch. In August 2011 it will again pass perihelion, expected to reach magnitude 9. However it will be very close to the sun at this time. In April/May it reached its greatest altitude of less than 10° for mid-European observers, expected to be only of magnitude 16-18. Michael Jäger succeeded in imaging the comet with his 10"-astrograph at the end of May, being just discernible. The comet will be better placed for observers near the equator, thus additional observations should be possible.
Only a small number of observations came to my knowledge. At the start of July 2011 the observers estimated the brightness between 10.5 mag and 12.0 mag, the coma diameter between 2' and 3.5' (IAUC 9219).
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Comet 49P/Arend-Rigaux (P=6.72a) will pass perihelion in mid-October 2011. Starting in mid-August it should be observable from mid-European latitudes. Brightening from 15 mag to 14 mag until the beginning of October it will move from the constellation Orion into Canis Minor, thereby gaining altitude in the morning sky. Typically this comet shows only a very faint coma, appearing almost stellar in smaller telescopes. The small number of published observations do not give a clear picture about the evolution of this comet during this apparition. On the one hand there are two observers who estimated a maximum brightness of 10.5 mag and a maximum coma diameter larger than 3.5' (175.000 km) (with one estimating even 6'). These observations can be best described using the parameters m0=6.5 mag/n=10 (resulting in a maximum brightness of 11.0 mag). On the other hand are five observers with estimates of 13.0 mag for the maximum brightness and a maximum coma diameter of about 1.5' (70.000 km). Their observations may be best described using the parameters m0=8.5 mag/n=10. During the apparition the coma seems to have grown more and more diffuse (at first: DC 3-4, at the end of the apparition: DC 2-3).
Total Brightness and Coma Diameter
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With larger instruments comet 123P/West-Hartley (P=7.58a) can be observed during spring 2011. It should be about magnitude 14.5, moving through the constellation Auriga, thus being an evening object. The few published observations yield a maximum brightness of 14.5 in May/June 2011 - just as predicted. The diameter of the medium condensed coma was in the order of 1'.
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During summer 2011 comet 213P/Van Ness (P=6.33a) should be observable with large amateur instruments. Predicted to be of magnitude 14.5 it moves from Pisces into Pegasus, being a morning sky object at the beginning and an object visible during the whole night at the end of summer.
The comet surprised in summer 2011: on July 29 H. Hanayama found a 20-21 mag fragment, named B, on images taken with the 1.05m-IAO-Teleskop within the tail. It was situated at a distance of 5.0' in p.a. 238° relative to the main component and showed a 1' tail. On Aug. 5. images taken with the Faulkes North telescope showed the fragment at the distance of 5.3' in p.a. 239°; it displayed a 5" coma and a 22" tail. In those days the comet showed also a 6' long needle-like anti-tail in p.a. 56°. During the days following the discovery component A was of magnitude about 12.0m, fragment B of magnitude 19.5. On Aug. 9 fragment B, elongated in the direction of the tail, had faded by half a magnitude, showing a 16" tail. The fragment was still discernible on Sep. 2. Calculations by Z. Sekanina indicate that the fragment separated during the perihelion passage of 2005, probably shortly prior to discovery, on July 25 or around Sep. 9 (CBET 2798 / MPEC 2011-P37, 2011-Q54 / Comet's Mailing List).
The unusual evolution of this comet was analyzed using 13 observations of 4 members of the German Comet Section and 85 international observations. According to the work by Z. Sekanina the largest fragment may have separated from the nucleus already during the previous perihelion passage. Images during the second week of September taken with larger instruments show two more fragments, C and D (Comet's mailing list). A brief brightness increase may well be associated with this separation, making a dt-formula plausible. The observations can be well described by the formula m = 10.7 mag + 5×log D + 0.017×|t-T|, resulting in a maximum brightness of about 12.0 mag. The clearly fainter observation at the beginning of June may well be the brightness before the increase. The apparent coma diameter increased during the documented apparition from 1.4' to 1.8' in mid-September, but seems to have decreased to 1.6' until the end of October. This yields a constant coma diameter of 100.000 km. The degree of condensation was at DC 3-4 until early September, decreasing thereafter, reaching DC 2 at the end of October.
Total Brightness and Coma Diameter
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Michael Jäger recognized a second outburst of comet 174P/Echeclus (P=35.3a) on an image of May 30, 2011. The comet showed an 1' coma of magnitude 15.0. Additional observations showed a faint spiral-like 40" coma with a central condensation of magnitude 18, from which a 6" jet in p.a. 60 60° originated (IAUC 9213). The coma was medium condensed (DC 4). This second observed outburst seems to have been short-lived. The last visual observations, of which I have knowledge, date from the end of June.
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On images taken for the Mt.Lemmon Survey on Dec. 17, 2011 a 19.5 mag object was found in the constellation Pegasus. Detailled observations during the following days indicated it was a comet. Comet P/2011 Y1 showed a 12" coma with a central condensation and a 14" tail towards p.a. 50°. Soon thereafter it became clear that this was the rediscovery of comet P/2006 T1 (Levy) - nearly 10 mag fainter than expected according to the 2006 apparition. This confirms the assumption that this comet was discovered during an outburst. The comet passed perihelion in mid-January 2012, but did not brighten more than 18.0 mag. For this comet the permanent designation 255P/Levy has been assigned (IAUC 9247 / MPEC 2012-B23).
Andreas Kammerer
