Water in the Near IR spectrum of Comet 8P/Tuttle

High resolution spectra of Comet 8P/Tuttle were obtained in the frequency range 3440.6–3462.6 cm on 3 January 2008 UT using CGS4 with echelle grating on UKIRT. In addition to recording strong solar pumped fluorescent (SPF) lines of H2O, the long integration time (152 minutes on target) enabled a number of weaker H2O features to be assigned, most of which had not previously identified in cometary spectra. These transitions, which are from higher energy upper states, are similar in character to the so-called ‘SH’ lines recorded in the post Deep Impact spectrum of Comet Tempel 1, suggesting an alternative production mechanism. We derive an H2O rotational temperature of 62±5K and a water production rate of (1.4±0.3)×10 molecules s.