Free access article

A&A 440, L21-L24 (2005)
DOI: 10.1051/0004-6361:200500160

Letter

Isotopic abundances of carbon and nitrogen in Jupiter-family and Oort Cloud comets

D. Hutsemékers¹, J. Manfroid¹, E. Jehin², C. Arpigny¹, A. Cochran³, R. Schulz⁴, J. A. Stüwe⁵ and J.-M. Zucconi<sup>6

1</sup>  Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 août 17, 4000 Liège, Belgium
    e-mail: hutsemekers@astro.ulg.ac.be
²  European Southern Observatory, Casilla 19001, Santiago, Chile
³  Department of Astronomy and McDonald Observatory, University of Texas at Austin, C-1400, Austin, USA
⁴  ESA/RSSD, ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands
⁵  Leiden Observatory, 2300 RA Leiden, The Netherlands
⁶  Observatoire de Besançon, 25010 Besançon Cedex, France

(Received 8 June 2005 / Accepted 21 July 2005 )

Abstract
The ¹²C¹⁴N/¹²C¹⁵N and ¹²C¹⁴N/¹³C¹⁴N isotopic ratios are determined for the first time in a Jupiter-family comet, 88P/1981 Q1 Howell, and in the chemically peculiar Oort Cloud comet C/1999 S4 (LINEAR). By comparing these measurements to previous ones derived for six other Oort Cloud comets (including one of Halley-type), we find that both the carbon and nitrogen isotopic ratios are constant within the uncertainties. The mean values are ¹²C/¹³C 90 and ¹⁴N/¹⁵N for the eight comets. These results strengthen the view that CN radicals originate from refractory organics formed in the protosolar molecular cloud and subsequently incorporated in comets.

Key words: comets: abundances -- comets: individual: 88P/Howell -- comets: individual: C/1999 S4 (LINEAR)

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