Recent searches for the radio lines of NH3 in comets
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: email@example.com
3 Radioastronomisches Institut, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
Accepted: 9 May 2005
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 3σ 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
© ESO, 2005