Comet 154P/Brewington (P=10.78a) will - for the third time since its discovery in 1992 - pass perihelion in November 2013. It should become observable with medium-sized instruments during summer 2013. It is positioned in Aquarius, moving northwestward. It will be an object in the morning sky at first, being observable during the whole night in October. According to the ICQ (brightness parameters: m₀=2.5 mag / n=12) the brightness should increase from 14.5 mag in July to 9.0 mag in mid-November. However, the comet evolved more slowly during its most recent apparition in 2002/03 (preliminary brightness parameters according to my analysis: m₀=7.0 mag / n=7), which would mean a maximum brightness of only 11.0 mag in early November.

During this apparition comet 154P/Brewington was not an easy object visually. The analysis is based on 60 observations by 6 members of the German Comet Section and 110 international observations. They indicate different brightness evolutions, pre- and post-perihelion. Pre-perihelion the brightness increased very rapidly, whereas the post-perihelion fading was much slower and can be best described by a dt-formula. The appropriate formulae are:

For a complete documentation I have to point to the fact that the observations of Uwe Pilz, dated Oct. 30, Nov. 24 and Dec. 30 are not included in the analysis since they are much too bright compared to the main data points. However, I have to admit, that his observation of Dec. 30 is supported by another person, which observed with him and by one international observer. Nevertheless I remain very sceptic since the comet displayed an extremely diffuse coma with its dimension hardly to discern. In addition, in my opinion it is physically not understandable that the international observer (who speaks of a brightness outburst) reports a brightness and coma diameter similar to the main body of observers for the following evening. Such a rapid change (for only a few hours) is difficult to explain for a comet at a distance of 1.6 AU from the Sun. In addition, the reported large coma diameters are not supported by photographs.

Total Brightness and Coma Diameter

The apparent coma diameter increased from 1.5' at first to a maximum value of 7.5' in the early days of November where it remained constantly for about 8 weeks. Thereafter it decreased steadily to 1.0' at the end of March 2014. The absolute coma diameter increased from 65.000 km at the start of the apparition to 350.000 in early November, thereafter continuing to increase more slowly until the end of December to the maximum value of 425.000 km. Starting at the end of December it decreased, reaching 120.000 km at the end of March 2014. During the whole period the coma remained quite diffuse, with a constant degree of condensation of DC 2.

Andreas Kammerer

FGK observations