The $^{{\sf 16}}$OH/$^{\sf 18}$OH and OD/OH isotope ratios in comet C/2002 T7 (LINEAR)

Abstract

The 16 OH/ 18 OH and OD/OH isotope ratios are measured in the Oort-Cloud comet C/2002 T7 (LINEAR) through ground-based observations of the OH A 2 Σ + − X 2 Πi ultraviolet bands at 3063 A (0, 0) and 3121 A (1, 1) obtained with the Very Large Telescope (VLT) feeding the Ultraviolet-Visual Echelle Spectrograph (UVES). From the 16 OH/ 18 OH ratio, we find 16 O/ 18 O = 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