144P/Kushida

It was expected that comet 144P/Kushida (P=7.60a) should become a rather easy evening object in winter 2008/09. Of magnitude 11 it would move from the eastern part of Aries into the eastern part of Taurus.

The comet showed a surprisingly positive evolution. During the days around Dec. 20 its brightness had already reached 9.0 mag – 1.5 mag brighter than expected! The brightness peaked at 8.5 mag around Jan. 20, 2009. Based on 40 reports by 8 members of the German Comet Section and additional 165 international observations (until the start of April 2009) an extreme, but surprisingly steady brightness evolution results, well described by the following formulae

The apparent coma diameter was only in the order of 1.5' during the first weeks, but increased during only one week to 9'! This enormous increase can not only be explained by the change from telescope to binoculars as instrument, but is an expression of the explosive increase of activity shortly before perihelion. The maximum value was held until the end of February, according to the estimates. However, the diagram shows a strangely long plateau, indicating that the coma diameter probably reached about 13-14', which went unnoticed due to the low surface brightness of the outer coma. From the beginning of March onwards the apparent coma diameter decreased slowly to 2.5' at the beginning of April. The absolute coma diameter was around 40.000 km during the first weeks, increasing due to the rapid expansion until the end of December to 225.000 km. Until the end of February it increased at a slower rate to 325.000 km. Thereafter the coma shrunk, measuring 175.000 km at the beginning of April. The coma was always quite diffuse with the degree of condensation rather constant at DC 2-3 to DC 3.

Total Brightness and Coma Diameter

Andreas Kammerer

FGK observations