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C/2011 M1 (LINEAR)


An asteroidal object of magnitude 18.5, discovered by the LINEAR project on June 22, 2011 in the constellation Andromeda showed its cometary nature in the course of more detailed observations. Comet C/2011 M1 (LINEAR) showed a compact 30" coma with a conspicious central condensation. Observations of June 24 showed a diffuse 2.3' coma of magnitude 14.5 mag and a 50" long narrow tail in p.a. 252°. On June 25 observers even noticed a diffuse 3.2' coma of magnitude 13.5 (IAUC 9218). The comet should pass perihelion at the beginning of September with a predicted maximum brightness of 11.0 mag. Until October it moved through the constellations Cassiopeia, Ursa Major into Leo, being comfortably placed at first, but situated at low altitudes after mid-August.

In the early days of November 2011 not more than 25 international observations document the evolution of this comet. The comet surprised with a high activity parameter which resulted in a maximum brightness of 9.6 mag during the first days of September. The brightness evolution can be well described by the formula

m = 9.5 mag + 5×log D + 18×log r

However, it has to be taken into account that the parameters are still uncertain, due to the small number of observations.

Total Brightness and Coma Diameter

According to the observers the coma diameter increased rapidly towards perihelion from 2' (150.000 km) to 6.5' (450.000 km). It is plausible to suppose a decrease until the end of September to 5' (375.00 km), but this is only supported by one single observation. The coma was always quite diffuse with the degree of condensation at DC 2.

Andreas Kammerer


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