A&A 439, 777-784 (2005)
DOI: 10.1051/0004-6361:20052801

Recent searches for the radio lines of NH in comets

J. Hatchell^{1, 2}, M. K. Bird³, F. F. S. van der Tak¹ and W. A. Sherwood<sup>1

1</sup>  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
²  School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
    e-mail: hatchell@astro.ex.ac.uk
³  Radioastronomisches Institut, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

(Received 1 February 2005 / Accepted 9 May 2005 )

Abstract
Radio observations in the ammonia inversion lines of four comets, C/2001 A2 (LINEAR), 153P/Ikeya-Zhang, C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), were performed at the Effelsberg 100-m Radio Telescope during their respective close approaches to Earth.

None of the four lowest energy metastable lines , could be detected in these comets. We derive the following 3 upper bounds on the NH₃ production rate , and comparing to the corresponding water production rates, percentage NH₃ abundances relative to H₂O:  s^-1 (0.63%) for C/2001 A2 (LINEAR),  s^-1 (0.13%) for C/2001 Q4 (NEAT),  s^-1 (0.74%) for C/2002 T7 (LINEAR) and  6.3 10²⁶ s^-1 (0.63%) for Comet 153P/Ikeya-Zhang. At 0.74% or less, the ammonia-to-water ratios are factors of ~2 below the value for C/1995 O1 (Hale-Bopp) and 1P/Halley, suggesting chemical diversity between comets. The 18-cm lines of OH were clearly detected in the two comets observed during the 2004 campaign, thereby validating the cometary ephemerides.

Key words: comets: individual: comet C/2001 A2 (LINEAR), comet 153P/Ikeya-Zhang, comet C/2001 Q4 (NEAT), comet C/2002 T7 (LINEAR) -- radio line: solar system

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© ESO 2005

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