Due to the fact that comet C/1997 J2 (Meunier-Dupouy) reached its minimum distance from earth in August (still 2.49 AU from our planet) this comet attained its second brightness peak. However, with 11.0m this one was not - as expected - brighter than the one at the end of 1997. The most probable explanation is that the gas production rate of comet Meunier-Dupouy decreased significantly since it reached perihelion. This is supported not only by the brightness evolution, but also by the fact that the coma diameter decreased from a maximum of 350.000 km at the end of 1997 to only 270.000 km in August 1998 and 1.5' (250.000 km) in mid-November. In addition the degree of condensation too was smaller this summer (DC 3-4) than at the end of 1997 (DC 4-5) and reached DC 2-3 in mid-November. As a conclusion it seems straightforward to suppose that comet Meunier-Dupouy experienced its greatest activity prior to perihelion, hinting at volatile gases as the main propellant of the gas production. Including 158 observations by 10 comet section members and 450 international observations the brightness evolution can be described by the following formulae:
pre-perihelion : m = 4.9m + 5×log D + 6.5×log r
post-perihelion: m = 2.8m + 5×log D + 11.3×log r
Total Brightness and Coma Diameter
These confirm that the activity of the comet decreased more rapidly after the perihelion passage. Due to the fact, that the differences in solar distance along the observed orbit are rather small, the parameters - especially the absolute magnitude - still exhibit a moderate standard deviation. The different absolute brightnesses have not much evidence, because comet Meunier-Dupouy did never came closer to the sun than 3 AU. The high absolute brightness and derived great diameter of the nucleus, however, are confirmed.
Andreas Kammerer
