Oxygen emission lines in the high resolution spectra of 9P/Tempel 1 following the Deep Impact event

Abstract

Context: On 2005 July 4, the NASA spacecraft Deep Impact delivered an impactor on the comet 9P/Tempel 1 to study the material ejected from the nucleus. A worldwide observation campaign accompanied the mission, to characterize the activity of 9P/Tempel 1 before and after the impact. Aims: At La Palma (Canary Islands), the comet was observed from July 2 to July 9 using the echelle spectrograph SARG on the Telescopio Nazionale Galileo (TNG). Fifteen spectra were obtained with a resolving power of R=29,000 in the spectral range 4620-7920 Å. Many interesting emission lines can be found in this range, in particular the [OI] lines at 5577 Å ("green line") and at 6300 and 6364 Å ("red doublet"). From the analysis of these lines it is possible to derive information on the processes that produce these emissions. Methods: The three atomic oxygen lines are clearly visible in most of the spectra. The intensity ratio between the green line and the sum of the red lines, indicative of the parent of these lines, was computed for 9 of the 15 spectra. The value of the intensity ratio for the night of July 5 was compared with the model results obtained from a coupled chemistry transport model. Results: The intensity ratio of green to red oxygen lines obtained from the observed spectra and the one derived from the model suggest water is the main parent of the [OI] emissions on comet 9P/Tempel 1.