| Abstract
| - High-resolution spectra of comet 8P/Tuttle were obtained in the frequency range 3449.0-3462.2 cm−1 on 2008 January 3 ut using CGS4 with echelle grating on United Kingdom Infrared Telescope. In addition to observing solar pumped fluorescent lines of H2O, the long integration time (152 min on target) enabled eight weaker H2O features to be assigned, most of which had not previously been 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. We have identified certain characteristics that these lines have in common, and which in addition to helping to define this new class of cometary line give some clues to the physical processes involved in their production. Finally, we derive an H2O rotational temperature of and a water production rate of (1.4 ± 0.3) × 1028 molecules s−1.
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