A Search for Variation in the H_2O Ortho-Para Ratio and Rotational Temperature in the Inner Coma of Comet C/2004 Q2 (Machholz)
Abstract
We present spatially resolved measurements of the rotational temperature and ortho-para ratio for H_2O in the inner coma of the Oort Cloud comet C/2004 Q2 (Machholz). Our results are based on direct simultaneous detections of ortho-H_2O and para-H_2O via "hot-band" fluorescence near 2.9 μm. We find a well-defined decline in rotational temperature with increasing nucleocentric distance (up to ~1000 km). The ortho-para ratio remains constant (within stochastic uncertainty) with increasing nucleocentric distance and is close to the statistical equilibrium value of 3.0 (2.86 ± 0.06 [0.17], including, respectively, stochastic [systematic] uncertainty), resulting in spin temperature T_(spin) ≥ 34 K. We compare the present results with those reported for other comets and discuss the difficulties in interpreting spin temperatures deduced from measured ortho-para ratios. Improved understanding of the special conditions that enable nuclear spin conversion would test the extent to which derived spin temperatures reflect the formative history or the processing record of cometary ices.
Additional Information
© 2007 The American Astronomical Society. Received 2007 January 5; accepted 2007 March 26; published 2007 April 24. We thank Jacques Crovisier for helpful comments. This work was supported by the NASA Planetary Astronomy Program under RTOP 344-32-30-07 to M. J. M. Our observations were conducted at the W. M. Keck Observatory, operated as a scientific partnership among Caltech, UCLA, and NASA. This observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors 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.Attached Files
Published - BONapjl07.pdf
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Additional details
- Eprint ID
- 16487
- Resolver ID
- CaltechAUTHORS:20091027-090044501
- RTOP 344-32-30-07
- NASA
- W. M. Keck Foundation
- Created
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2009-10-29Created from EPrint's datestamp field
- Updated
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2021-11-08Created from EPrint's last_modified field