ABSTRACT. We present high-dispersion infrared spectra of hydroxyl (OH) in comets C/2000 WM₁ (LINEAR) and C/2004 Q2 (Machholz), acquired with the Near Infrared Echelle Spectrograph at the Keck Observatory atop Mauna Kea, Hawaii. Most of these rovibrational transitions result from photodissociative excitation of H₂O giving rise to OH "prompt" emission. We present calibrated emission efficiencies (equivalent g-factors, measured in OH photons s^-1 [H₂O molecule]^-1) for more than 20 OH lines sampled in these two comets. The OH transitions analyzed cover a broad range of rotational excitation. This infrared database for OH can be used in two principal ways: (1) as an indirect tool for obtaining water production in comets simultaneously with the production of other parent volatiles, even when direct detections of H₂O are not available; and (2) as an observational constraint to models predicting the rotational distribution of rovibrationally excited OH produced by water photolysis.

Subject headings: comets: general; comets: individual (C/2000 WM1 [LINEAR], C/2004 Q2 [Machholz]); infrared: solar system; molecular data

Print publication: Issue 1 (2006 December 10)
Received 2006 May 18, accepted for publication 2006 August 9