An object near the border of Perseus/Taurus, reported as asteroidal by LINEAR on Nov. 19, 2003 showed a 2" coma when observed near Year's end. In mid-January 2004 the diameter of the coma of magnitude 17.5 was measured as 8". Comet C/2003 WT42 (LINEAR) will not pass perihelion until spring 2006 (IAUC 8280). Because it will not get any closer than about 5 A.U. it was expected to brighten to only about magnitude 15.
According to 60 international observations the comet reached maximum brightness of 13.4 mag in February 2006. The brightness evolution can be well described with the parameters m0=3.0m / n=4. However, the brightness parameters m0=6.5m / n=2 or m0=-0.6m / n=6 simulate the evolution equally well (due to the very small variance in solar distance). During the apparition the apparent coma diameter increased steadily from 0.5' to 1.1' (first days of May 2006). In contrast, the absolute coma diameter was rather constant at about 140.000 km until March 2006. Thereafter it increased to 240.000 km in May 2006. The degree of condensation was constant at DC 5.
Total Brightness and Coma Diameter
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Another asteroidal object, this time of magnitude 16.5 and positioned near the border of the constellations Serpens/Libra, was discovered on May 6, 2005. Detailed observations showed a faint 1' coma. Comet P/2005 JQ5 (Catalina), having a very faint absolute magnitude, passed perihelion at the end of July, passing earth at the end of June at a distance of only 0.10 AU (IAUC 8531). Moving from Virgo into Cancer it was expected to reach a maximum brightness of magnitude 12, alas at very low altitudes. The comet showed a morphology very similar to that of comet P/2002 EX12=169P/NEAT, namely an extreme diffuse and large coma with low surface brightness and a small central condensation. Accordingly brightness estimates were difficult. Maximum brightness was somewhere between 9.5 mag and 10.5 mag. Michael Jäger and Gerald Rhemann measured a 1' coma of magnitude about 14.5 on a CCD image on May 25. On June 6 the coma was of magnitude 13.5, showing a very diffuse 5-6' coma. On June 12/13 they estimated a brightness of 12.0-12.5 mag, measuring a 2.5' oval inner coma and an extremely diffuse 7-8' outer coma; in addition two short tails - pointing in opposite directions - were noticed. On June 24/25 the coma showed a diameter of almost 10' on their CCD image. Terry Lovejoy estimated the extremely diffuse comet on a picture taken the same night at magnitude 9-10 mag, measuring a coma diameter of 20'. Juan Jose Gonzalez succeeded in observing the comet visually at an altitude of only 11° on the following night (June 25/26), using a 20 cm SCT telescope. He could discern a coma of 4' diameter, which he estimated to be of magnitude 10.3. However he was sure that the coma actually was larger (Comet's Mailing List). After its perihelion the comet was unfavourably placed for mid-European latitudes at first. On Aug. 13/14 Jäger/Rhemann estimated its brightness to be 12.5 mag with a 2.5' coma (altitude less than 15°). Based on these estimates the brightness parameters can roughly be derived as m0=15.0m / n=4. The coma measured only 50.000 km in diameter at perigee.
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On May 16, 2005 B.A. Skiff discovered a 17.0 mag comet in the constellation Draco. Comet C/2005 K1 (Skiff) showed a 16" moderately condensed coma and a 90" long tail in p.a. 325°; additional observers even measured a 1.3' coma. The comet will pass perihelion in November 2005, but should reach maximum brightness of about 15.5 mag already during late summer (IAUC 8532). Observers estimated the comet to be of magnitude 14.0-14.5 during summer/fall 2005. The coma with a diameter of about 0.7' was moderately condensed.
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On May 20, 2005 R. McNaught discovered just another comet in the course of the Siding Spring Survey. Positioned in the eastern parts of Aquarius the 17.0 mag object displayed a miniscule coma and a 30" long, narrow tail in p.a. 240°. Comet P/2005 K3 (McNaught) orbits the sun with a period of 10.1 years. It will pass perihelion in August, expected to be of magnitude 15.5 at that time (IAUC 8535, MPEC 2005-L42). According to the estimates published during summer 2005 the comet is about 1.5 mag brighter than expected. At the start of September it was of magnitude 13.5, displaying a 0.5' coma (DC 5).
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On Sep. 10, 2005 M.E. Van Ness discovered a 16.0 mag comet on images taken by the LONEOS-telescope. Comet P/2005 R2 (Van Ness) presented a 20" large coma with a 245" long tail at PA=240°. The comet, orbiting the sun with a period of 6.3 years, passed its perihelion already in February 2005 (calculated brightness: 16.0 mag, but close to the Sun), so that a slow decrease in brightness was expected (IAUC 8597 / MPEC 2005-U05). On Sep. 24/25 Jäger/Rhemann imaged the comet with their 8"SC and a SXV-CCD Camera as a 14.5 mag object. On Oct. 9/10 Dieter Schubert could successfully observe the comet with his 203/812 mm Schmidt-Newton and a Meade DSI CCD Camera, finding a coma diameter of 0.5' and a short tail of 0.6' in p.a. 241°, estimating the brightness roughly at 12-13 mag. On Oct. 29/30 Dieter Schubert observed this comet again: the comet showed such a small coma that it was not possible to measure reliably, the brightness was estimated at about 14 mag. International observations between the end of October and the beginning of November indicate a slight increase in brightness from 13.5 mag to 13.0 mag. The well-condensed coma showed an apparent diameter of 1.0' After this outburst-period the comet faded slowly during winter 2005/06.
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R.D. Matson and M. Mattiazzo independently reported a possible comet, found in the SWAN data of the first half of October 2005, located in the constellation Ophiuchus. Earthbound observations with larger instruments, beginning on Oct. 22 showed a moderately condensed, fan-shaped coma of about 2' diameter. On Oct. 23 Alan Hale estimated comet P/2005 T4 (SWAN) visually at magnitude 12.1 with a diffuse 1.5' coma. CCD-observations by Terry Lovejoy on Oct. 18 yielded a brightness of 12 mag. Michael Jäger found it with his 8" Schmidt-Camera at magnitude 12.0 with a 1.0' coma on the evening of Oct. 29. The comet, intrinsically very faint, passed perihelion in the first days of October. Additional astrometric observations yielded an orbit with a period of 27.3 years (IAUC 8619/24, MPEC 2005-V22). Since the comet was rather close to Earth at discovery, receeding fast since then, its brightness decreased rapidly during the following weeks.
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A well-developped comet of magnitude 17 with a 20" tail towards WNW was discovered by R. Hill on Catalina Survey images of Jan. 6, 2006 in the constellation Sextans. Later it was realized that the comet is identical with an asteroidal object discovered by LONEOS in the constellation Hydra on Dec. 4, 2005. Comet P/2005 XA54 (LONEOS-Hill) passed perihelion in March 2006, not expected to get brighter than 16 mag. Surprisingly it was estimated 2 mag brighter during February/March 2006. The comet orbits the sun with a period of 15.2 years (IAUC 8656).
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Only 40 international estimates could be used for the analysis of the apparition of comet 21P/Giacobini-Zinner. These indicate a brightness evolution according to the formula m = 9.0m + 5×log D + 15×log r, yielding a maximum brightness of 10.0 mag during the first days of July 2005. The coma showed a constant diameter of 2.0' (140.000 km), with the coma moderately condensed (DC 4).
Total Brightness and Coma Diameter
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Regarding the brigthness evolution comet 32P/Comas Sola fulfilled the predictions as is shown by 13 observations by 3 members of the German Comet Section and 65 additional international ones. The estimates can be described quite well by the formula m = 9.7m + 5×log D + 8×log r, resulting in a maximum brightness of 12.8 mag during the second half of December 2004. The apparent coma diameter increased from almost 1.0' in October 2004 to a maximum of 1.4' at the beginning of January 2005. Thereafter it decreased, reaching 1.0' again in April. The absolute coma diameter increased from 60.000 km to a maximum of 90.000 km at the start of February 2005. Thereafter it decreased slowly, reaching 80.000 km at the beginning of April. The degree of condensation was DC 4-5 at the beginning of the apparition, decreasing to DC 2-3 until the beginning of March, where it then remained.
Total Brightness and Coma Diameter
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Only 20 international reports could be used for analysing the 2005 apparition of comet 37P/Forbes. They indicate a brightness evolution according to the formula m = 9.8m + 5×log D + 15×log r. Thus the peak brightness of 12.0 mag was reached at the beginning of July 2005. The coma diameter increased from 0.7' (20.000 km) to 1.1' (40.000 km). The degree of condensation was rather constant at DC 2-3.
Total Brightness and Coma Diameter
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Comet 49P/Arend-Rigaux exhibits cometary activity only occassionally. In 2004/05 it did and so it could be observed during February/March 2005. The few estimates hint to a maximum of 13.0 mag in the first half of March and a coma diameter of about 0.8'. The degree of condensation was estimated between 2 and 3.
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Comet 60P/Tsuchinshan reached a maximum of 15.5 mag during winter 2005/06, showing a coma of diameter 1.0'.
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Contrary to the very bright apparition of comet 69P/Taylor in 1997 (when it reached 11 mag) in 2004/05 this comet was in a normal state and therefore only of magnitude 15. International observations showed the comet at magnitude 16 at the beginning of January 2005, with a coma diameter of about 1'.
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On Nov. 30, 2005 E.J. Christensen discovered a significantly condensed 15" object at a distance of only 21.5' (dt = -0.9d) ahead of the presumed 16.5 mag primary component of comet 101P/Chernykh. This secondary component was of magnitude 18.0, showing a central condensation and a broad 10-15" tail in p.a. 57° (IAUC 8637). According to the fragmentation modell of Z. Sekanina this fragment is not identical with the one observerd in 1991/92. In fact it separated from the primary at the end of 1996 (± 3 months), at a solar distance of 8-9 AU.
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Observers of comet 117P/Helin-Roman-Alu estimated it 1 mag brighter than expected during summer 2005. The coma had a diameter slightly larger than 0.5' and a maximum brightness of 13.8 mag. Thus it seemed plausible that the comet should be at a similar magnitude during summer 2006 (after perihelion passage in Dec. 2005). Unfortunately it would then be located in the southern parts of the constellation Aquarius.
Michael Jäger and Gerald Rhemann photographed it end of May 2006. It was of magnitude 14, showing a 20" coma and a 15' tail.
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On Feb. 27, 2005 Michael Jaeger succeeded in recovering the component A of comet 141P/Machholz at a very low altitude. He and a few visual observers estimated the comet to be of magnitude about 12.0 (IAUC 8495). The diameter of the very diffuse (DC 2) coma was estimated to be about 1'. No trace was detected of component D.
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An asteroidal object of magnitude 20, discovered already on March 15, 2002 by the NEAT team in the constellation Virgo, showed comet-like activity when observed at the end of July 2005. Two independent observers reported a tail up to 77" long in p.a. 145°, but no coma. Comet P/2002 EX12 (NEAT) passed perihelion of its 4.2 year orbit in mid-September 2005, approaching Earth within 0.15 AU at the beginning of August, when its starlike condensation became as bright as 14.5 mag (IAUC 8578). Meanwhile it was found on images reaching back to 1988, therefore receiving the permanent designation 169P/NEAT (IAUC 8591). According to CCD images taken by Michael Jäger und Gerald Rhemann the comet reached a maximum brightness of 11.5 mag and a maximum coma diameter of 5' in mid-August. In addition, they could record a tail up to 10' long. Based on the small number of published estimates the brightness parameters can be deduced roughly as m0=16.0m / n=8. Overall their images show a strong resemblance of the comets 2002 EX12 and 2005 JQ5: both had a large and extremely faint coma when close to Earth.
Andreas Kammerer
