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Title: Near-UV OH Prompt Emission in the Innermost Coma of 103P/Hartley 2

Abstract

The Deep Impact spacecraft flyby of comet 103P/Hartley 2 occurred on 2010 November 4, 1 week after perihelion with a closest approach (CA) distance of about 700 km. We used narrowband images obtained by the Medium Resolution Imager on board 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 on board Deep Impact . 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 emissionmore » process where photodissociation of H{sub 2}O directly produces excited OH*( A {sup 2}Σ{sup +}) 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.« less

Authors:
 [1]; ; ; ; ; ; ;  [2]
  1. Department of Physics and Astronomy, University of Padova, Vicolo dellOsservatorio 3, I-35122 Padova (Italy)
  2. Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States)
Publication Date:
OSTI Identifier:
22663130
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 154; Journal Issue: 5; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMETS; DATA ANALYSIS; DENSITY; DISSOCIATION; DISTRIBUTION; DUSTS; FLUORESCENCE; ICE; IMAGES; PHOTOLYSIS; RADICALS; RESOLUTION; SPACE VEHICLES; WATER; WATER VAPOR

Citation Formats

La Forgia, Fiorangela, Bodewits, Dennis, A’Hearn, Michael F., Protopapa, Silvia, Kelley, Michael S. P., Sunshine, Jessica, Feaga, Lori, and Farnham, Tony, E-mail: fiorangela.laforgia@unipd.it. Near-UV OH Prompt Emission in the Innermost Coma of 103P/Hartley 2. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA8E03.
La Forgia, Fiorangela, Bodewits, Dennis, A’Hearn, Michael F., Protopapa, Silvia, Kelley, Michael S. P., Sunshine, Jessica, Feaga, Lori, & Farnham, Tony, E-mail: fiorangela.laforgia@unipd.it. Near-UV OH Prompt Emission in the Innermost Coma of 103P/Hartley 2. United States. doi:10.3847/1538-3881/AA8E03.
La Forgia, Fiorangela, Bodewits, Dennis, A’Hearn, Michael F., Protopapa, Silvia, Kelley, Michael S. P., Sunshine, Jessica, Feaga, Lori, and Farnham, Tony, E-mail: fiorangela.laforgia@unipd.it. Wed . "Near-UV OH Prompt Emission in the Innermost Coma of 103P/Hartley 2". United States. doi:10.3847/1538-3881/AA8E03.
@article{osti_22663130,
title = {Near-UV OH Prompt Emission in the Innermost Coma of 103P/Hartley 2},
author = {La Forgia, Fiorangela and Bodewits, Dennis and A’Hearn, Michael F. and Protopapa, Silvia and Kelley, Michael S. P. and Sunshine, Jessica and Feaga, Lori and Farnham, Tony, E-mail: fiorangela.laforgia@unipd.it},
abstractNote = {The Deep Impact spacecraft flyby of comet 103P/Hartley 2 occurred on 2010 November 4, 1 week after perihelion with a closest approach (CA) distance of about 700 km. We used narrowband images obtained by the Medium Resolution Imager on board 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 on board Deep Impact . 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{sub 2}O directly produces excited OH*( A {sup 2}Σ{sup +}) 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.},
doi = {10.3847/1538-3881/AA8E03},
journal = {Astronomical Journal (Online)},
number = 5,
volume = 154,
place = {United States},
year = {Wed Nov 01 00:00:00 EDT 2017},
month = {Wed Nov 01 00:00:00 EDT 2017}
}