GALEX FUV OBSERVATIONS OF COMET C/2004 Q2 (MACHHOLZ): THE IONIZATION LIFETIME OF CARBON

Journal Article · Sat Jan 01 04:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/726/1/8· OSTI ID:21567737

Morgenthaler, Jeffrey P ^[1]; Harris, Walter M ^[2]; Combi, Michael R ^[3]; Feldman, Paul D ^[4]

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1. Planetary Science Institute, 1700 E. Fort Lowell, Suite 106, Tucson, AZ 85719 (United States)
2. Department of Applied Sciences, University of California at Davis, One Shields Ave., Davis, CA 95616 (United States)
3. Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, 2455 Hayward St., Ann Arbor, MI 48109 (United States)
4. Department of Physics and Astronomy, Johns Hopkins University, Charles and 34th Street, Baltimore, MD 21218 (United States)

We present a measurement of the lifetime of ground state atomic carbon, C({sup 3}P), against ionization processes in interplanetary space and compare it to the lifetime expected from the dominant physical processes likely to occur in this medium. Our measurement is based on analysis of a far ultraviolet (FUV) image of comet C/2004 Q2 (Machholz) recorded by the Galaxy Evolution Explorer (GALEX) on 2005 March 1. The bright C I 1561 A and 1657 A multiplets dominate the GALEX FUV band. We used the image to create high signal-to-noise ratio radial profiles that extended beyond 1 x 10{sup 6} km from the comet nucleus. Our measurements yielded a total carbon lifetime of (7.1-9.6) x 10{sup 5} s (ionization rate of (1.0-1.4) x 10{sup -6} s{sup -1}) when scaled to 1 AU. This compares favorably to calculations assuming solar photoionization, solar wind proton change exchange, and solar wind electron impact ionization are the dominant processes occurring in this medium and that comet Machholz was embedded in the slow solar wind. The shape of the C I profiles inside 3 x 10{sup 5} km suggests that either the CO lifetime is shorter than previously thought and/or a shorter-lived carbon-bearing parent molecule, such as CH{sub 4}, is providing the majority of the carbon in this region of the coma of comet Machholz.

• OSTI ID: 21567737
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 726; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
79 ASTRONOMY AND ASTROPHYSICS
ALKANES
CARBON
CARBON COMPOUNDS
CARBON MONOXIDE
CARBON OXIDES
CHALCOGENIDES
COMETS
DIMENSIONLESS NUMBERS
ELECTROMAGNETIC RADIATION
ELEMENTS
FAR ULTRAVIOLET RADIATION
HYDROCARBONS
IMAGES
INTERPLANETARY SPACE
IONIZATION
LIFETIME
METHANE
NONMETALS
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOIONIZATION
RADIATIONS
SIGNAL-TO-NOISE RATIO
SOLAR ACTIVITY
SOLAR WIND
SPACE
STELLAR ACTIVITY
STELLAR WINDS
ULTRAVIOLET RADIATION