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Large-Aperture [O I] 6300 A Photometry of Comet Hale-Bopp: Implications for the Photochemistry of OHLarge-aperture photometric observations of comet Hale-Bopp (C/1995 O1) in the forbidden red line of neutral oxygen ([O I] 6300 angstroms) with the 150 mm dual-etalon Fabry-Perot spectrometer that comprises the Wisconsin H-alpha Mapper and a 50 mm dual-etalon Fabry-Perot spectrometer at the McMath-Pierce main telescope from 1997 late February to mid April yield a total metastable O((sup 1)D) production rate of (2.3-5.9) x 10(exp 30)/s. Applying the standard H2O and OH photodissociation branching ratios, we derive a water production rate, Q(H2O), of (2.6-6.1) x 10(exp 31)/s, which disagrees with Q(H2O = 1x10(exp 31)/s determined by independent H2O, OH, and H measurements. Furthermore, our own [O I] 6300 observations of the inner coma (< 30,000 km) using the 3.5 m Wisconsin-Indiana-Yale-NOAO telescope Hydra and Densepak multi-object spectrographs yield Q(H2O) = 1 x 10(exp 31)/s. Using our [O I] 6300 data, which cover spatial scales ranging from 2,000 to 1x10(exp 6) km, and a complementary set of wide-field ground-based OH images, we can constrain the sources of the apparent excess O((sup 1)D) emission to the outer coma, where photodissociation of OH is assumed to be the dominant O((sup 1)D) production mechanism. From production rates of other oxygen-bearing volatiles (e.g., CO and CO2), we can account for at most 30% of the observed excess O((sup 1)D) emission. Since even less O((sup 1)D) should be coming from other sources (e.g., electron excitation of neutral O and distributed nonnuclear sources of H2O), we hypothesize that the bulk of the excess O((sup 1)D) is likely coming from photodissociating OH. Using the experimental OH photo-dissociation cross section of Nee and Lee at Ly-alpha as a guide in modifying the theoretical OH cross sections of van Dishoeck and Dalgarno, we can account for approximately 60% of the observed O((sup 1)D) excess without requiring major modifications to the other OH branching ratios or the total OH photodissociation lifetime.
Document ID
20020014289
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Morgenthaler, Jeffrey P.
(Wisconsin Univ. Madison, WI United States)
Harris, Walter M.
(Wisconsin Univ. Madison, WI United States)
Scherb, Frank
(Wisconsin Univ. Madison, WI United States)
Anderson, Christopher M.
(Wisconsin Univ. Madison, WI United States)
Oliversen, Ronald J.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Doane, Nathaniel E.
(National Solar Observatory United States)
Combi, Michael R.
(Michigan Univ. Ann Arbor, MI United States)
Marconi, Maximus L.
(Fresh Pond Research Inst. Cambridge, MA United States)
Smyth, William H.
(Atmospheric and Environmental Research, Inc. United States)
Date Acquired
August 20, 2013
Publication Date
December 10, 2001
Publication Information
Publication: Astrophysical Journal
Publisher: American Astronomical Society
Volume: 563
Subject Category
Astronomy
Funding Number(s)
CONTRACT_GRANT: NASW-97020
CONTRACT_GRANT: NAG5-7952
CONTRACT_GRANT: NSF AST-96-15625
Distribution Limits
Public
Copyright
Other

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