O(1S) and O(1D) emission lines in the spectrum of 153P/2002 C1 (Ikeya-Zhang)

High resolution spectroscopy observation of comet 153P/2002 C1 Ikeya-Zhang was performed on April 20, 2002 with the echelle spectrograph SARG on the 3.5 m Telescopio Nazionale Galileo in La Palma. The atomic O emission lines at 5577, 6360 and 6363 angstrom are clearly visible in the spectrum. We determined the intensity ratio of the green line to the sum of the red lines. In order to verify the hypothesis that water is the main parent species of these emissions, the result was compared with the value obtained from a coupled chemistry-transport model. The measured value for the green to red ratio, 0.12 +/- 0.1, agrees quite well with the value obtained from the model. This led us to conclude that during the observation water was the parent species of atomic O lines.