Reference : Survey for Ortho-to-Para Abundance Ratios (OPRs) of NH2 in Comets: Revisit to the Mea...
Scientific congresses and symposiums : Paper published in a journal
Physical, chemical, mathematical & earth Sciences : Space science, astronomy & astrophysics
Survey for Ortho-to-Para Abundance Ratios (OPRs) of NH2 in Comets: Revisit to the Meaning of OPRs of Cometary Volatiles
Kawakita, Hideyo [Koyama Astronomical Observatory, Kyoto Sangyo Univ]
Shinnaka, Yoshiharu [National Astronomical Observatory of Japan]
Jehin, Emmanuel mailto [Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa) >]
Decock, Alice [Institut d’Astrophysique et de Géophysique, Université de Liège]
Hutsemekers, Damien mailto [Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS) >]
Manfroid, Jean mailto [Université de Liège > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO) >]
Bulletin of the American Astronomical Society
American Astronomical Society
New York
48th DPS Meeting
16-21 October 2016
[en] comets ; solar system
[en] Since molecules having identical protons can be classified into nuclear-spin isomers (e.g., ortho-H[SUB]2[/SUB]O and para-H[SUB]2[/SUB]O for water) and their inter-conversions by radiative and non-destructive collisional processes are believed to be very slow, the ortho-to-para abundance ratios (OPRs) of cometary volatiles such as H[SUB]2[/SUB]O, NH[SUB]3[/SUB] and CH[SUB]4[/SUB] in coma have been considered as primordial characters of cometary molecules [1]. Those ratios are usually interpreted as nuclear-spin temperatures although the real meaning of OPRs is in strong debate. Recent progress in laboratory studies about nuclear-spin conversion in gas- and solid-phases [2,3] revealed short-time nuclear-spin conversions for water, and we have to reconsider the interpretation for observed OPRs of cometary volatiles. We have already performed the survey for OPRs of NH[SUB]2[/SUB] in more than 20 comets by large aperture telescopes with high-resolution spectrographs (UVES/VLT, HDS/Subaru, etc.) in the optical wavelength region [4]. The observed OPRs of ammonia estimated from OPRs of NH[SUB]2[/SUB], cluster around ~1.1 (cf. 1.0 as a high-temperature limit), indicative of ~30 K as nuclear-spin temperatures. We present our latest results for OPRs of cometary NH[SUB]2[/SUB] and discuss about the real meaning of OPRs of cometary ammonia, in relation to OPRs of water in cometary coma. Chemical processes in the inner coma may play an important role to achieve un-equilibrated OPRs of cometary volatiles in coma.This work was financially supported by MEXT Supported Program for the Strategic Research Foundation at Private Universities, 2014–2018 (No. S1411028) (HK) and by Graint-in-Aid for JSPS Fellows, 15J10864 (YS).References:[1] Mumma & Charnley, 2011, Annu. Rev. Astro. Astrophys. 49, 471.[2] Hama & Watanabe, 2013, Chem. Rev. 113, 8783.[3] Hama et al., 2008, Science 351, 6268.[4] Shinnaka et al., 2011, ApJ 729, 81.
Researchers ; Professionals ; Students

File(s) associated to this reference

Fulltext file(s):

Restricted access
2016DPS....4833003S.pdfPublisher postprint339.12 kBRequest copy

Bookmark and Share SFX Query

All documents in ORBi are protected by a user license.