On Mar. 14, 2009 the Japanese amateur Koichi Itagaki found a 11 mag comet near the border of the constellations Cetus/Aries while scanning CCD images with a software that recognizes moving objects automatically. Comet C/2009 E1 (Itagaki) showed a diffuse 70" coma with a faint central condensation and a hint of a tail in southerly directions. Visual observations showed the comet in those days to be of magnitude 9.5 to 10.0 with a 4' coma. The comet, rounding the Sun on an elliptical 250 years orbit, could be verified on images taken in the ultraviolet by the SWAN probe (IAUC 9026/27, MPEC 2009-G12).
The comet showed an interesting brightness evolution, as indicated by 3 observations by 2 members of the German Comet Section and additional 50 international observations. According to these the brightness increased rapidly prior to perihelion, decreasing much more slower afterwards. The maximum brightness of 7.9 mag was reached at perihelion. The brightness evolution can be described by the following formulae:
pre-perihelion: m = 12.4 mag + 5×log D + 22.5×log r post-perihelion: m = 9.1 mag + 5×log D + 8.4×log rThe coma diameter measured about 5' (240.000 km) at first, decreasing rapidly to 3' (180.000 km) in mid-May, being constant thereafter. The degree of condensation increased from DC4 to DC 5 at maximum brightness. Thereafter the coma got more diffuse, reaching DC 1-2 at the beginning of June.
Total Brightness and Coma Diameter
Andreas Kammerer
