The 16OH/18OH and OD/OH isotope ratios in comet C/2002 T7 (LINEAR)

The 16OH/18OH and OD/OH isotope ratios are measured in the Oort-Cloud comet C/2002 T7 (LINEAR) through ground-based observations of the OH ultraviolet bands at 3063 A (0,0) and 3121 A (1,1) secured with the Very Large Telescope (VLT) feeding the Ultraviolet-Visual Echelle Spectrograph (UVES). From the 16OH/18OH ratio, we find 16O/18O = 425 +/- 55, equal within the uncertainties to the terrestrial value and to the ratio measured in other comets, although marginally smaller. We also estimate OD/OH from which we derive D/H = 2.5 +/- 0.7 10-4 in water. This value is compatible with the water D/H ratios evaluated in other comets and marginally higher than the terrestrial value.