Cyanogen Jets and the Rotation State of Comet Machholz (C/2004 Q2)

Abstract

Extensive observations of Comet Machholz (C/2004 Q2) from 2005 February, March, and April were used to derive a number of the properties of the comet's nucleus. Images were obtained using narrowband comet filters to isolate the CN morphology. The images revealed two jets that pointed in roughly opposite directions relative to the nucleus and changed on hourly timescales. The morphology repeated itself in a periodic manner, and this fact was used to determine a rotation period for the nucleus of 17.60 ± 0.05 hr. The morphology was also used to estimate a pole orientation of R.A. = 50°, decl. = +35°, and the jet source locations were found to be on opposite hemispheres at mid-latitudes. The longitudes are also about 180° apart, although this is not well constrained. The CN features were measured to be moving at about 0.8 km s-1, which is close to the canonical value typically quoted for gas outflow. Future modeling of the CN features will be used to improve and extend these results.