Ground-Based Detection of Deuterated Water in Comet C/2014 Q2 (Lovejoy) at IR Wavelengths

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 × 10(exp 29) and 3.6 +/- 1.0 × 10(exp 26) molecules/sec, respectively. The simultaneous detection permitted accurate determination of the isotopic ratio (D/H) in water of 3.02 +/- 0.87 × 10(exp −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.