Analysis of past comet apparitions

C/2008 C1 (Chen-Gao)


On Feb. 1, 2008 Xing Gao discovered a 13 mag comet in the constellation Cepheus on images done in the course of a private nova search (initiated by both observers) by Tao Chen. A check of additional images revealed the comet on Jan. 30 (14.0 mag) and 31 (13.5 mag). An image on Feb. 2 showed the comet at 12.0 mag. Comet C/2008 C1 (Chen-Gao) showed a 2.5' coma, elongated in p.a. 40° and presenting a significant central condensation (IAUC 8915/16). The comet will pass perihelion in mid-April 2008, at predicted magnitude 12. However, since the indicated observations hint towards an outburst the further brightness evolution is uncertain. It will disappear for mid-European observers in mid-May, after passing through Perseus, Auriga, Taurus, Orion and Monoceros.

For the analysis 11 observations by 4 members of the German Comet Section and 75 international observations could be used. These indicate a large activity parameter n, according to the formula

m = 6.1m + 5×log D + 27.5×log r

This yields a discovery brightness of 13.5 mag and a maximum brightness of 9.7 mag during the second week of April. Starting at the beginning of April, however, the estimates are situated systematically below this trend.

Total Brightness and Coma Diameter

The coma diameter increased from 1' at discovery to 5' in mid-March. This value was kept until the end of the apparition. The absolute coma diameter measured 75.000 km at the start of the apparition, increasing rapidly to 275.000 km until the start of March. Thereafter the increase continued at a much slower pace, reaching 325.000 km at the beginning of May. The degree of condensation was rather constant at DC 3 during the whole apparition.

Andreas Kammerer

FGK observations


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