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Near-UV OH Prompt Emission in the Innermost Coma of 103P/Hartley 2
- Publication Year :
- 2017
- Publisher :
- arXiv, 2017.
-
Abstract
- The Deep Impact spacecraft fly-by of comet 103P/Hartley 2 occurred on 2010 November 4, one week after perihelion with a closest approach (CA) distance of about 700 km. We used narrowband images obtained by the Medium Resolution Imager (MRI) onboard the spacecraft to study the gas and dust in the innermost coma. We derived an overall dust reddening of 15\%/100 nm between 345 and 749 nm and identified a blue enhancement in the dust coma in the sunward direction within 5 km from the nucleus, which we interpret as a localized enrichment in water ice. OH column density maps show an anti-sunward enhancement throughout the encounter except for the highest resolution images, acquired at CA, where a radial jet becomes visible in the innermost coma, extending up to 12 km from the nucleus. The OH distribution in the inner coma is very different from that expected for a fragment species. Instead, it correlates well with the water vapor map derived by the HRI-IR instrument onboard Deep Impact \citep{AHearn2011}. Radial profiles of the OH column density and derived water production rates show an excess of OH emission during CA that cannot be explained with pure fluorescence. We attribute this excess to a prompt emission process where photodissociation of H$_2$O directly produces excited OH*($A^2\it{\Sigma}^+$) radicals. Our observations provide the first direct imaging of Near-UV prompt emission of OH. We therefore suggest the use of a dedicated filter centered at 318.8 nm to directly trace the water in the coma of comets.<br />Comment: 21 pages
- Subjects :
- Physics
Earth and Planetary Astrophysics (astro-ph.EP)
Jet (fluid)
010504 meteorology & atmospheric sciences
comets: individual (103P/Hartley 2)
methods: data analysis
techniques: photometric
Resolution (electron density)
Photodissociation
Comet
FOS: Physical sciences
Astronomy and Astrophysics
Coma (optics)
Astrophysics
01 natural sciences
Fluorescence
Space and Planetary Science
Excited state
0103 physical sciences
010303 astronomy & astrophysics
Water vapor
Astrophysics - Earth and Planetary Astrophysics
0105 earth and related environmental sciences
Subjects
Details
- Database :
- OpenAIRE
- Accession number :
- edsair.doi.dedup.....57fd52acdc32c6cc8ea76b6f4f6feb2b
- Full Text :
- https://doi.org/10.48550/arxiv.1709.08931