The Gas Production of Comet 9P/Tempel1 around the Deep Impact Date

Abstract

The target of the Deep Impact space mission (NASA), comet 9P/Tempel1, was observed from two nights before impact to eight nights after impact using the FORS spectrographs at the ESO VLT UT1 and UT2 telescopes. Low resolution optical long-slit spectra were obtained to study the evolution of the gas coma around the Deep Impact event. Following first results of this observing campaign on the CN and dust activity (Rauer et al. 2006), this work presents a study of the complete dataset on CN, C₂, C₃ and NH₂ activity of comet 9P/Tempel1. An extended impact gas cloud was observed moving radially outwards. No compositional differences between this impact cloud and the undisturbed coma were found as far as the observed radicals are concerned. The gas production rates before and well after impact indicate no change in the cometary activity on an intermediate time scale. Over the observing period, the activity of comet 9P/Tempel 1 was found to be related to the rotation of the cometary nucleus. The rotational light curve for different gaseous species provides indications for compositional differences among different parts of the nucleus surface.