Postperihelion spectra and images of comet Wilson (1986l) obtained with a focal reducer

Abstract

Comet Wilson (1986l) was observed with the MPAE/Hoher List focal reducer-based CCD camera and grism spectrometer having spectral resolution of 4.9 Å per pixel, coupled to the ESO 1-m reflector. The data base consists of six long slit spectra, one of them is taken on the nucleus and the others at 1.5 × 10 5 km in the tail, and images with filters centered at 6600 and 4250 Å. A “ray” structured tail longer than 400,000 km is detected in the emissions of CO +. The H 2O +/CO + ratio in the tail is found 1.7±0.2 at 51,000 km and 1.6 ± 0.2 at 150,000 km from the nucleus. The H 2O + flux at a distance of 150,000 km in the tail changed by a factor of 0.4 within 3 hr of our observations. The continuum profile extracted from the spectrum centered on the nucleus shows a distinct sunward asymmetry. From the imaging data we see that most of the dust ejection occurs in a “beam” on the sunward side, producing a “fan” like structure. The particles in the dust fan are redder than the solar color. Most of the particles are redder by ∼8–9% per 1000 Å, the highest being ∼10% per 1000 Å. The maximum reddened area is situated at a distance of ∼7 × 10 4 km from the nucleus in the northeast direction. The fan is about 7° wide and originates at about 12° east of the subsolar point. The dust column density derived from the spectrum centered on the nucleus is found to be asymmetric in the sun-antisun direction and deviates from π −1 dependence at ∼12,000 km on the sunward side and at ∼4000 km in the tailward direction. The water production rate derived from the [OI] flux is 2.7 ± 1.8 × 10 29 molecules/ sec. The C 2 and NH 2 production rates are 0.5 ± 0.1 × 10 27 and 0.8 ± 0.2 × 10 26 molecules/sec.