Comet 22P/Kopff: Dust Environment and Grain Ejection Anisotropy from Visible and Infrared Observations

Moreno, Fernando; Pozuelos, Francisco; Aceituno, Francisco; Casanova, Víctor; Sota, Alfredo; Castellano, Julio; Reina, Esteban
The Astrophysical Journal, Volume 752, Issue 2, article id. 136, 12 pp. (2012).


We present optical observations and Monte Carlo models of the dust coma, tail, and trail structures of the comet 22P/Kopff during the 2002 and 2009 apparitions. Dust loss rates, ejection velocities, and power-law size distribution functions are derived as functions of the heliocentric distance using pre- and post-perihelion imaging observations during both apparitions. The 2009 post-perihelion images can be accurately fitted by an isotropic ejection model. On the other hand, strong dust ejection anisotropies are required to fit the near-coma regions at large heliocentric distances (both inbound at rh = 2.5 AU and outbound at rh = 2.6 AU) for the 2002 apparition. These asymmetries are compatible with a scenario where dust ejection is mostly seasonally driven, coming mainly from regions near subsolar latitudes at far heliocentric distances inbound and outbound. At intermediate to near-perihelion heliocentric distances, the outgassing would affect much more extended latitude regions, the emission becoming almost isotropic near perihelion. We derived a maximum dust production rate of 260 kg s-1 at perihelion, and an averaged production rate over one orbit of 40 kg s-1. An enhanced emission rate, also accompanied by a large ejection velocity, is predicted at rh > 2.5 pre-perihelion. The model has also been extended to the thermal infrared in order to be applied to available trail observations of this comet taken with IRAS and Infrared Space Observatory spacecrafts. The modeled trail intensities are in good agreement with those observations, which is remarkable taking into account that those data are sensitive to dust ejection patterns corresponding to several orbits before the 2002 and 2009 apparitions.