Gas and dust in Comet 2P/Encke observed in the visual and submillimeter wavelength ranges

Abstract

In November 2003 Comet 2P/Encke was observed simultaneously with the 10-m Heinrich–Hertz Submillimeter Telescope on Mount Graham, Arizona, USA, and the 2-m optical telescope on Mount Rozhen, Bulgaria. Simultaneous radio observations of the 4–3 and 3–2 rotational transitions of HCN and the 0–0 transition of the CN violet band system provide a three-dimensional view on the comet. The observations are consistent with outgassing from the source region I with location and pole position of Comet Encke taken from [14]. The outflow speed is 1.2 km. There is some evidence for another possible parent for CN besides HCN. The visual dust coma of Comet Encke is nearly spherical with a diameter of about 1000 km and a slight extension into Comet Encke’s fan. The polarization of the observed NH₂ transition at 662 nm is 7% at a phase angle of 94.5°, close to the value for two-atomic molecules. At this phase angle and a wavelength of 642 nm the polarization of Comet Encke’s dust is greater than 30%, i.e., exceeds the value for so-called dusty comets.