The carbon isotope abundance ratio in comet Halley

Abstract

view Abstract Citations (30) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Carbon Isotope Abundance Ratio in Comet Halley Kleine, Marvin ; Wyckoff, Susan ; Wehinger, Peter A. ; Peterson, Bruce A. Abstract The isotope abundance ratio for carbon, C-12/C-13, in the coma gas of comet Halley was determined by observing the fluorescence spectrum of the CN radical. The optical spectra of the R-branch of the CN B2Sigma(+)-X2Sigma(+) (0,0) band covered the spectral range from 3683 to 3877 A at a resolution of approximately 75,000. Spectral reduction and analysis techniques were developed and described for extracting the coma spectrum with optimal signal-to-noise characteristics from the long-slit spectral images. These techniques led to the identification of four C-13 N-14 lines, Ri(5), Ri(6), Ri(8) in the spectrum of comet Halley. New rotational line flourescence efficiency factors were computed for all stable isotopic species of CN to facilitate observers in C-12 N-15. We give ratios of fluorescence efficiencies for all stable isotopic species of CN to facilitate observers in predicting the most favorable helicentric velocities for determining carbon and nitrogen isotopic abundance ratios in CN fluorescence spectra of comets. Based on our reanalysis of the spectrum of comet Halley, we have determined a C-12 N-14/C-13 N-14 isotope ratio for the bulk coma gases of 95 +/- 12. This result agrees with the solar carbon isotope abundance ratio of 90, and supersedes a previous value determined for comet Halley. The absence of C-12 N-15 line features in our comet spectrum is consistent with a nitrogen isotopic abundance ratio at least as large as the solar value. The agreement of the carbon isotope ratio derived for comet Halley with the solar value provides evidence that comets coevolved from the same molecular cloud as other members of the solar system. Publication: The Astrophysical Journal Pub Date: February 1995 DOI: 10.1086/175239 Bibcode: 1995ApJ...439.1021K Keywords: Abundance; Carbon Isotopes; Halley'S Comet; Mass Ratios; Charge Coupled Devices; Data Reduction; Giotto Mission; Resonance Fluorescence; Spectrographs; Spectrum Analysis; Lunar and Planetary Exploration; COMETS: INDIVIDUAL NAME: HALLEY; MOLECULAR PROCESSES; SOLAR SYSTEM: GENERAL; SUN: ABUNDANCES full text sources ADS |