Comet P/grigg-Skjellerup: Ground-based observations after the encounter with the Giotto spacecraft

Abstract

After the encounter with the Giotto spacecraft, the comet P/Grigg-Skjellerup was observed with the 2.2 m ESO telescope. Imaging in theV andR bands and infrared photometry with theJ andH filters were performed. From the radial enhancement of the images we derived that theR frame mainly concerns the dust tail of the comet. Thus we applied the inverse numerical method of dust tail analysis in order to estimate the following cometary-grain parameters: ejection velocity, anisotropy of the emission, size distribution and loss rate. This from the observations back in time to the Giotto encounter. From infrared observation we could calculate theJ andH magnitudes and the colour indexJ−H=0.4 consistent with previous measurements of the comet.