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Title: {sup 14}NH{sub 2}/{sup 15}NH{sub 2} RATIO IN COMET C/2012 S1 (ISON) OBSERVED DURING ITS OUTBURST IN 2013 NOVEMBER

We performed high-dispersion optical spectroscopic observations of comet C/2012 S1 (ISON) using the High Dispersion Spectrograph (R = 72,000) at the Subaru Telescope on UT 2013 November 15.6, during an outburst that started on UT 2013 November 14. Due to the high gas-production rate of NH{sub 2} during the outburst, we successfully detected weak emission lines of {sup 15}NH{sub 2} and many strong emission lines of {sup 14}NH{sub 2} in the optical wavelength region from 5500 to 8200 Å. The ratio of {sup 14}NH{sub 2}/{sup 15}NH{sub 2} is derived to be 139 ± 38 in comet C/2012 S1 (ISON). This ratio is close to that recently revealed based on the averaged spectrum of 12 comets, ∼130. This is also comparable to the typical cometary isotopic ratio of CN ({sup 12}C{sup 14}N/{sup 12}C{sup 15}N, observed in optical) and HCN (H{sup 12}C{sup 14}N/H{sup 12}C{sup 15}N, observed in radio), ∼150. However, these ratios are much smaller than the protosolar value, {sup 14}N/{sup 15}N = 441 ± 5. Because NH{sub 2} is considered to be a photodissociation product of NH{sub 3} in cometary coma, our result implies the occurrence of {sup 15}N fractionation of NH{sub 3} in the solar nebula or in the presolarmore » molecular cloud.« less
Authors:
; ; ;  [1] ;  [2]
  1. Koyama Astronomical Observatory, Kyoto Sangyo University, Motoyama, Kamitamo, Kita, Kyoto 603-8555 (Japan)
  2. Scientific Studies and Consulting, 171 Harmon Drive, San Antonio, TX 78209 (United States)
Publication Date:
OSTI Identifier:
22363987
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 782; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMMONIA; ASTRONOMY; ASTROPHYSICS; CARBON 12; CARBON NITRIDES; COMETS; COMPARATIVE EVALUATIONS; DISSOCIATION; EMISSION SPECTRA; INTERSTITIAL HELIUM GENERATION; INTERSTITIAL HYDROGEN GENERATION; ISOTOPE RATIO; MOLECULES; NITROGEN 14; NITROGEN 15; SOLAR NEBULA; TELESCOPES