2017ApJ...836L..25P

We conducted a deep search for deuterated water (HDO) in the Oort Cloud comet C/2014 Q2 (Lovejoy), through infrared (IR) spectroscopy with NIRSPEC at the Keck Observatory. In this Letter, we present our detections of HDO and water (H₂O) in comet Lovejoy on 2015 February 4 (post-perihelion) after 1 hr integration on source. The IR observations allowed simultaneous detection of H₂O and HDO, yielding production rates of 5.9 ± 0.13 x 10²⁹ and 3.6 ± 1.0 x 10²⁶ molecules s^–1, respectively. The simultaneous detection permitted accurate determination of the isotopic ratio (D/H) in water of 3.02 ± 0.87 x 10^–4, i.e., larger than the value for water in terrestrial oceans (or Vienna Standard Mean Ocean Water, VSMOW) by a factor of 1.94 ± 0.56. This D/H ratio in water exceeds the value obtained independently at millimeter wavelengths (0.89 ± 0.25 VSMOW; pre-perihelion). We discuss these parameters in the context of origins and emphasize the need for contemporaneous measurements of HDO and H₂O.