Reference : Ortho-to-para Abundance Ratio (OPR) of Ammonia in 15 Comets: OPRs of Ammonia Versus 1...
Scientific journals : Article
Physical, chemical, mathematical & earth Sciences : Space science, astronomy & astrophysics
http://hdl.handle.net/2268/10367
Ortho-to-para Abundance Ratio (OPR) of Ammonia in 15 Comets: OPRs of Ammonia Versus 14N/15N Ratios in CN
English
Shinnaka, Yoshiharu [Kyoto Sangyo University, Department of Physics, Facility of Science, Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555, Japan]
Kawakita, Hideyo [Kyoto Sangyo University, Department of Physics, Facility of Science, Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555, Japan]
Kobayashi, Hitomi [Kyoto Sangyo University, Department of Physics, Facility of Science, Motoyama, Kamigamo, Kita-ku, Kyoto 603-8555, Japan]
Jehin, Emmanuel mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique et traitement de l'image]
Manfroid, Jean mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO)]
Hutsemekers, Damien mailto [Institut d'Astrophysique et de Géophysique Liège Université, Université de Liège, B-4000 Liège, Belgium ; FRS-FNRS, Université de Liège, B-4000 Liège, Belgium]
Arpigny, Claude mailto [Université de Liège - ULg > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO)]
1-Mar-2011
Astrophysical Journal
University of Chicago Press
729
81, pp. 1-15
Yes (verified by ORBi)
International
0004-637X
1538-4357
Chicago
IL
[en] comets: general ; ISM: clouds ; ISM: molecules ; protoplanetary disks
[en] The ortho-to-para abundance ratio (OPR) of cometary molecules is considered to be one of the primordial characteristics of cometary ices. We present OPRs of ammonia (NH[SUB]3[/SUB]) in 15 comets based on optical high-dispersion spectroscopic observations of NH[SUB]2[/SUB], which is a photodissociation product of ammonia in the gaseous coma. The observations were mainly carried out with the VLT/UVES. The OPR of ammonia is estimated from the OPR of NH[SUB]2[/SUB] based on the observations of the NH[SUB]2[/SUB] (0, 9, 0) vibronic band. The absorption lines by the telluric atmosphere are corrected and the cometary C[SUB]2[/SUB] emission lines blended with NH[SUB]2[/SUB] lines are removed in our analysis. The ammonia OPRs show a cluster between 1.1 and 1.2 (this corresponds to a nuclear spin temperature of ~30 K) for all comets in our sample except for 73P/Schwassmann-Wachmann 3 (73P/SW3). Comet 73P/SW3 (both B- and C-fragments) shows the OPR of ammonia consistent with nuclear spin statistical weight ratio (1.0) that indicates a high-temperature limit as nuclear spin temperature. We compared the ammonia OPRs with other properties ([SUP]14[/SUP]N/[SUP]15[/SUP]N ratios in CN, D/H ratios of water, and mixing ratios of volatiles). Comet 73P/SW3 is clearly different from the other comets in the plot of ammonia OPRs versus [SUP]14[/SUP]N/[SUP]15[/SUP]N ratios in CN. The ammonia OPRs of 1.0 and lower [SUP]15[/SUP]N-fractionation of CN in comet 73P/SW3 imply that icy materials in this comet formed under warmer conditions than other comets. Comets may be classified into two groups in the plot of ammonia OPRs against [SUP]14[/SUP]N/[SUP]15[/SUP]N ratios in CN.
Researchers
http://hdl.handle.net/2268/10367
10.1088/0004-637X/729/2/81
http://adsabs.harvard.edu/abs/2011ApJ...729...81S

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