ESO Spectrophotometry of Comet 9 P / Tempel 1

The Deep Impact target comet 9P/Tempel 1 was observed by means of longslit spectroscopy from two nights before impact up to eight nights after impact, using the ESO VLT UT1, UT2, and ESO NTT telescopes. Spectra covering the complete optical wavelength range were obtained, and information at different position angles in the coma was collected. The data were used to study the gas and dust activity of comet 9P/Tempel 1. Gas production rates before and after impact and the amount of material in the impact cloud were determined. The pre-impact Afρ parameter, the dust production rate and the dust-to-gas mass ratio were derived. A variation of the cometary gas activity with rotation of the nucleus was detected. A difference in the variation of the brightness of the CN gas emission band compared to the variation of the emissions by C2, C3, and NH2 in the inner coma suggests compositional differences between different parts of the surface of comet 9P/Tempel 1’s nucleus.