On Jan. 29, 2004 NEAT reported an asteroidal object of magnitude 19 in Orion. Detailled observations during the following day showed a 3" coma, elongated towards p.a. 300-320° (IAUC 8279). Comet C/2004 B1 (LINEAR) was still at a solar distance of nearly 8 A.U. at discovery date and will not pass perihelion until February 2006. Assuming n=4 it could brighten to magnitude 9-10 during the first half of 2006. Assuming n=3 it could still become a 11 mag object. However, it will not be visible from mid-Europe prior to April of that year.
Only 22 visual observations of the comet could be used for the analysis, resulting in only rough results of its brightness evolution. It can be described with only one formula by assuming an activity parameter around zero (m0=11.5m / n=0). Thus the derived maximum brightness is 12 mag in May 2006. However, estimates in fall 2005 give a similar brightness. Additional CCD-observations seem to indicate a sudden drop in brightness of about 1 mag in mid-August 2006. At the beginning of the apparition the coma had a diameter of 1.5' (125.000 km), but in spring 2006 only a little more than 1.0' (75.000 km) was estimated. In parallel it got more condensed (DC 2-3 to DC 3-4) during this time.
Total Brightness and Coma Diameter
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An asteroidal object of magnitude 18.5, already discovered on Apr. 20, 2006 in the course of the Siding Spring Survey near the border of the constellations Aquarius/Capricorn, showed cometary activity during a more detailed study at the end of July. While images taken on July 26 showed a stellar object, on July 29 comet P/2006 HR30 (Siding Spring) showed a faint 10" coma, elongated in p.a. 31°. Images taken on Aug. 4 documented an asymmetric coma or a tail of 10" length in p.a. 5-10°. The comet with a period of 21.9 years will pass perihelion at the end of 2006 and might get as bright as 10.5 mag (IAUC 8735/37).
A photograph taken by Jäger/Rhemann on Aug. 18 also showed a noticeable narrow tail. In contrast, during the first days of September CCD observers found only a stellar object of magnitude 13.5 without a tail.
Only 35 observations can be used for the analysis. These hint towards a very unusual brightness evolution. Until the end of September 2006 the comet brightened, thereafter remaining constant between 14.0 mag and 14.5 mag until at least mid-February 2007. This implies a negative parameter n, that means the activity of the comet decreased while approaching the sun. However, the fact that a tiny coma could only be detected during the very first weeks of the apparition implies, that the comet showed cometary behaviour only during this short time intervall, thereafter behaving like an ordinary asteroid. Actually, the brightness evolution can be simulated with the asteroidal brightness parameters H=12.0 / G=0.15!
Total Brightness and Coma Diameter
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On June 14, 2006 Robert McNaught discovered a comet in the course of the Siding Spring Survey. Comet C/2006 L2 (McNaught) was of magnitude 13.5, situated in Centaurus. It displayed a 40" coma and a 1.5' tail in p.a. 135°. Observations on June 15 showed a conspicious star-like false nucleus and a 25" coma, elongated in p.a. 140°. A visual observation by John Bortle on the same day showed a 0.7' diffuse coma of magnitude 13.5. Similar estimates were published until the end of July. The comet will pass perihelion at the end of November, possibly reaching 13.0 mag (IAUC 8721).
Analyzing 25 observations can only yield rough results. The brightness evolution can be represented by the parameters m0= 4.0 mag / n=7, implying a maximum brightness of 11.5 mag during the second half of December 2006. The coma diameter increased slowly from 1.0' (100.000 km) at the beginning of the apparition to a maximum of 2.0' (200.000 km), but had decreased to 1.5' (150.000 km) in mid-March 2007. The degree of condensation was constant at DC 3.
Total Brightness and Coma Diameter
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An apparently asteroidal object of magnitude 17.5, already discovered on Dec. 9, 2006 by the LINEAR-team near the border of the constellations Cassiopeia/Perseus, showed cometary activity at closer inspection at the start of January 2007. Comet C/2006 XA1 (LINEAR) showed a 24" coma with a faint central condensation and a 10" tail in p.a. 310°. It will pass perihelion in July 2007, expected to reach magnitude 14.5. However, during this period it will be situated very near the sun. According to the current elements it rounds the sun about every 4000 years (IAUC 8790 / MPEC 2007-C33). Michael Jäger observed it on Feb. 9, 2007 as a 15.5-16.0 mag object with a 1' coma. On the evening of Mar. 11 he could photograph it with an 8"SC plus CCD as an object of 14.5 mag with a 1.5' coma. At the beginning of April the brightness of the 1' coma was estimated as 13.5 mag visually.
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Comet 41P/Tuttle-Giacobini-Kresak (P = 5.4a) was recovered on Feb. 3, 2006 by LINEAR and on Feb. 24, 2006 in the course of the Mt.Lemmon Surveys - the first observations since 2001, which forced minor modifications of the orbital elements. Images on Feb. 24 showed a 15x20" coma (major axis towards p.a. 100/280°) of magnitude 17.0 (IAUC 8679). Due to its extremely high activity parameter (n=16) it could be accessed with amateur instruments during spring 2006. While moving from Gemini into Virgo it was expected to peak at about magnitude 11.0. However this comet is known to experience short-lived outbursts up to nearly 10 magnitudes!
Analyzing 30 international observations yields different brightness evolutions prior and post-perihelion:
pre-perihelion: m = 9.3m + 5×log D + 37×log r post-perihelion: m = 9.6m + 5×log D + 20×log rresulting in a maximum brightness of 10.0 mag in mid-June. The coma diameter increased from almost 1' (40.000 km) in mid-May to 4.5' (100.000 km) in the second half of June, thereafter decreasing to almost 2' (100.000 km) until the end of August. The coma was only moderately condensed (DC 3).
Total Brightness and Coma Diameter
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Michael Jäger and Gerald Rhemann recovered comet 45P/Honda-Mrkos-Pajdusakova in Pisces on May 24, 2006 from Namibia. The comet was of magnitude 11, exhibiting a moderately condensed 2' coma. It will pass perihelion end of June, being positioned too near the sun for the next months.
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Comet 71P/Clark was recovered by several obseratories at the end of December 2005. Positioned in the eastern parts of Virgo it was of magnitude 17.5-18.0 (IAUC 8652). For a first analysis 40 international observations could be used, which indicate a very asymmetric brightness evolution. The heliocentric magnitude increased until 40 days after perihelion; the evolution can be described only by dt-formulae:
t < +40d: m = 12.3m + 5×log D - 0.025×|t-T| t > +40d: m = 10.7m + 5×log D + 0.020×|t-T|
Total Brightness and Coma Diameter
A maximum brightness of 10.2 mag in mid-June results. The coma diameter increased from almost 1.0' (40.000 km) at the beginning of May to 1.8' (50.000 km) in mid-July. Thereafter it decreased to about 1.0' (35.000 km) at the end of August. The coma was moderately condensed (DC 4-5). For mid-European observers the comet will appear above the southern evening horizon at the beginning of October 2006 as an object of magnitude 13.5. Until the beginning of December it will move from the constellation Microscope to the southern parts of Aquarius, thus becoming better placed, but fading.
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On Aug. 25, 2006 comet 76P/West-Kohoutek-Ikemura was recovered in Orion (MPEC 2006-Q61). According to the ICQ-Handbook it should reach magnitude 13-14 at the end of 2006. The very small number of observations indicate a maximum brightness of about 13 mag.
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Michael Jäger and Gerald Rhemann recovered comet 80P/Peters-Hartley on May 2006 during their astronomy vacances in Namibia. Positioned in Hydra, the 19 mag comet showed a faint 15" coma with a diffuse central condensation. It will pass perihelion in September at an expected magnitude of 14-15, but will then be situated near the sun.
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On B-, V-, R- and I-band-images with the 5m-telescope at Mt. Palomar of the centaur (60558) 2000 EC98 on Dec. 30, 2005 a coma is definitely visible. On the R-band-images a 20" coma of magnitude 17.5 can be seen (the calculated magnitude of the object was then 20-21 mag). The object will pass perihelion (r = 5.9 AU) of its 35.3 year orbit on Apr. 24, 2015 (IAUC 8656). Observations on Jan. 10, 2006 showed a condensed 1' coma of magnitude 14.0-14.5, but no tail. Visual estimates during January and early February confirm this magnitude (IAUC 8660). Amateur instruments show a rather diffuse coma of 0.5' diameter. Thus this centaur at a current solar distance of 13.0 AU is the most distant comet ever observed visually. In the meantime it was designated 174P/Echeclus (P = 35.3a) (the same name which was already assigned to the asteroid).
On CCD images taken on Apr. 2, the cometary object showed a complex morphology: a 2' coma of low surface brightness east of the nucleus and a 7" region of high surface brightness west of the nucleus, which was most probably the result of a short-lived outburst. Whereas the nucleus was of magnitude R=20.1, the low surface region was of magnitude 16 and the high surface region of magnitude 17.9 (IAUC 8677, 8701).
Michael Jäger and Gerald Rhemann photographed the comet on May 20 and 23, 2006 on their visit to Namibia. It was of magnitude 16.0, displaying an elongated 1.5' coma, which showed a diffuse central condensation.
In the meantime several scientific groups presented an explanation for the odd morphology of this object. According to them it is a binary object with a great and very active fragment and a nearly inactive primary. On Dec. 30, 2005 the brightness of the two components was 20.7 mag (primary) and 16.1 mag (secondary), separated by only 1.4". At the end of February 2006 the maximum separation of 7.0" was reached, thereafter closing to 2.7" by May 4 (CBET 563).
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On Jan. 11, 2007 three observers of the Sofia observatory recovered comet P/2001 Q2 (Petriew) near the border of the constellations Corvus/Virgo.Comet P/2007 A3 (Petriew) = 185P/Petriew was of magnitude 16.0, showing a 0.7' coma (with an inner coma of diameter 15-20"). The correction to the predictions was only dt = -0.04d (IAUC 8795/96 and 8803). The comet is expected to reach 14 mag, but is unfavorably placed for mid-European observers. Michael Jäger observed the comet on Feb. 9 as a 12.0 mag object (2.5 mag brighter than expected) with a condensed 1.5' coma. During February/March 2007 the comet was observed visually. It was of magnitude 11.5, displaying a 1.5' medium-condensed coma.
Andreas Kammerer
