A comprehensive study of infrared OH prompt emission in two comets. I. Observations and effective g-factors

Creators: Bonev, Boncho P.; Mumma, Michael J.; DiSanti, Michael A.; Russo, Neil Dello; Magee-Sauer, Karen; Ellis, Richard S.; Stark, Daniel P.

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 H_2O giving rise to OH "prompt" emission. We present calibrated emission efficiencies (equivalent g-factors, measured in OH photons s^(-1) [H_2O 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 H_2O are not available; and (2) as an observational constraint to models predicting the rotational distribution of rovibrationally excited OH produced by water photolysis.

Additional Information

© 2006 The American Astronomical Society. Received 2006 May 18; accepted 2006 August 9. We thank our anonymous referee for providing helpful comments. We also thank Geronimo L. Villanueva and Philip B. James for useful discussions on the presented results, and Harold Weaver for his assistance with the C/2000 WM1 observations. This work was supported by the NASA Planetary Astronomy Program under RTOP 344-32-30-07 to M. J. M., and RTOP 344-32-98 toM. A. D.; by NASA Planetary Atmospheres Program grants NAG5-10795 and NAG5-12285 to N. D. R.; and by RTOP 344-33-55 to M. A. D. K. M.-S. acknowledges support from the National Science Foundation RUI Program (0407052). The data presented herein were obtained at the W. M. Keck Observatory, operated as a scientific partnership among the California Institute of Technology, University of California at Los Angeles, and NASA. This observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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