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Study of the Forbidden Oxygen Lines in Comets at Different Heliocentric and Nucleocentric Distances
Decock, Alice; Rousselot, P.; Jehin, Emmanuel et al.
2013In Bulletin of the American Astronomical Society, 45, p. 502.08
 

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Abstract :
[en] Oxygen is an important element in the chemistry of the solar system objects given its abundance and its presence in many molecules including H2O 80% of cometary ices). The analysis of oxygen atoms in comets can provide information not only on the comets themselves but also on the solar system. These atoms have been analyzed using the 3 forbidden oxygen lines [OI] observed in emission in the optical region at 5577.339 Å (the green line), 6300.304 Å and 6363.776 Å (the red lines) (Swings, 1962). Our analysis is based on a sample of 12 comets of various origins. The observing material is made of 53 high signal-to-noise spectra obtained with the high-resolution UVES spectrograph at the ESO VLT from 2002 to 2012 (Manfroid et al, 2009). After noticing that the green line is blended with one C2 line, we built synthetic spectra of C2 for each observing circumstances and we subtracted its contribution to the cometary spectra in order to ensure the decontamination of the 5577 Å line. Then, we measured the intensity of the 3 [OI] lines at different heliocentric distances. By comparing the green to red lines ratio (G/R) with the Bhardwaj & Raghuram (2012) effective excitation rates, we found that H2O is the main parent molecule when the comet is observed at 1 au. When the comet is located beyond 2.5 au from the Sun, CO2 also contributes to the production of oxygen. Studying forbidden oxygen lines could be a new way to estimate the abundances of CO2 in comets, a very difficult task from the ground (Decock et al. 2013). In order to estimate the effect of the quenching on our results, we analyzed the evolution of the G/R ratio at different nucleocentric distances. For nearby comets, we divided the extended 2D spectrum into several zones in order to analyze the oxygen lines as close as possible to the nucleus (down to ~10 km for the closest comets). Their analysis will allow us to study the link of the oxygen lines with the nucleocentric distance. We found a clear variation of the G/R ratio close to the comet nucleus that is in agreement with a contribution from CO2 as predicted by Raghuram & Bhardwaj (2013).
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Decock, Alice ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Rousselot, P.;  Université de Franche-Comté, Observatoire des Sciences de l’Univers THETA, Institut UTINAM, France
Jehin, Emmanuel  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Hutsemekers, Damien ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Manfroid, Jean  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO)
Bhardwaj, A.;  Space Physics Laboratory, India
Raghuram, S.;  Space Physics Laboratory, India)
Language :
English
Title :
Study of the Forbidden Oxygen Lines in Comets at Different Heliocentric and Nucleocentric Distances
Publication date :
01 October 2013
Event name :
45th DPS Meeting
Event date :
6-11 October 2013
Audience :
International
Journal title :
Bulletin of the American Astronomical Society
ISSN :
0002-7537
eISSN :
2330-9458
Publisher :
American Astronomical Society, New York, United States - New York
Special issue title :
45th DPS Meeting
Volume :
45
Pages :
502.08
Available on ORBi :
since 10 October 2013

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