Letter to the Editor

Isotopic abundance of nitrogen and carbon in distant comets ^*

¹ Institut d'Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, 4000 Liège, Belgium e-mail: manfroid@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 Observatoire de Besançon, 25010 Besançon Cedex, France
⁵ ESA/RSSD, ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands
⁶ Leiden Observatory, 2300 RA Leiden, The Netherlands

Received: 13 December 2004
Accepted: 20 January 2005

Abstract

The ¹²C¹⁴N/¹²C¹⁵N and ¹²C¹⁴N/¹³C¹⁴N  isotopic ratios have been determined in comets C/1995 O1 (Hale-Bopp), C/2001 Q4 (NEAT) and C/2003 K4 (LINEAR) at heliocentric distances of, respectively, 2.7, 3.7 and 2.6 AU. These ratios have also been measured at AU. No significant differences were found between all determinations, nor with the value obtained for other comets. If confirmed, the discrepancy between the nitrogen isotopic ratios from optical and millimeter measurements on CN and HCN would rule out HCN as a major parent of the cometary CN radicals.