High resolution spectra of Comet 8P/Tuttle were obtained in the frequency range 3449.0–3462.2 cm ^ { -1 } on 3 January 2008 UT using CGS4 with echelle grating on UKIRT .
In addition to observing solar pumped fluorescent ( SPF ) lines of H _ { 2 } O , the long integration time ( 152 minutes on target ) enabled eight weaker H _ { 2 } O 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 ( Barber et al. , 2007 ) .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 H _ { 2 } O rotational temperature of 62 \pm 5 \mathrm { K } and a water production rate of ( 1.4 \pm 0.3 ) \times 10 ^ { 28 } molecules s ^ { -1 } .