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Astron. Astrophys. 353, 1101-1114 (2000)


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New molecules found in comet C/1995 O1 (Hale-Bopp)

Investigating the link between cometary and interstellar material

D. Bockelée-Morvan 1, D.C. Lis 2, J.E. Wink 3, D. Despois 4, J. Crovisier 1, R. Bachiller 5, D.J. Benford 2, N. Biver 6, P. Colom 1, J.K. Davies 7, E. Gérard 1, B. Germain 1, M. Houde 8, D. Mehringer 9, R. Moreno 3, G. Paubert 10, T.G. Phillips 2 and H. Rauer 11

1 Observatoire de Paris, 92195 Meudon, France
2 California Institute of Technology, MS 320-47, Pasadena, CA 91125, USA
3 Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 Grenoble, France
4 Observatoire de Bordeaux, B.P. 89, 33270 Floirac, France
5 Instituto Geográfico Nacional, Observatorio Astronómico Nacional, Apartado 1143, 28800 Alcalá de Henares, Spain
6 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
7 Joint Astronomy Centre, 680 North A'Ohoku Place, University Park, Hilo, HI 96720-6030, USA
8 Caltech Submillimeter Observatory, 111 Novelo Street, Hilo, HI 96720, USA
9 University of Illinois, Department of Astronomy, 1002 W. Green St., Urbana, IL 61801, USA
10 Instituto de Radioastronomía Millimétrica, Avenida Divina Pastora 7, Núcleo Central, 18012 Granada, Spain
11 DLR, Institute of Space Sensor Technology and Planetary Exploration, Rutherford Strasse, 12484 Berlin, Germany

Received 19 July 1999 / Accepted 2 November 1999

Abstract

We present millimetre and submillimetre observations of comet C/1995 O1 (Hale-Bopp) undertaken near perihelion with the Caltech Submillimeter Observatory and the 30-m telescope and Plateau-de-Bure interferometer of the Institut de Radioastronomie Millimétrique. From a spectral molecular survey, six new cometary molecular species have been identified for the first time in a comet: SO, SO2, HC3N, NH2CHO, HCOOH, and HCOOCH3. Relative abundances with respect to water are 0.3% (SO), 0.2% (SO2), 0.02% (HC3N), 0.01-0.02% (NH2CHO), 0.09% (HCOOH), and 0.08% (HCOOCH3). Several rotational transitions of OCS and HNCO, whose first identifications were made previously in comet C/1996 B2 (Hyakutake), have also been detected, confirming that these molecular species are ubiquitous compounds of cometary atmospheres. Inferred abundances of OCS and HNCO relative to water in comet Hale-Bopp are 0.4% and 0.1%, respectively. During this observational campaign, we also observed rotational lines of HCN, HNC, CH3CN, CO, CH3OH, H2CO, H2S, and CS. In combination with results of other observations, a comprehensive view of the volatile composition of the coma of comet Hale-Bopp is obtained. A quantitative comparison shows that chemical abundances in comet Hale-Bopp parallel those inferred in interstellar ices, hot molecular cores and bipolar flows around protostars. This suggests that the processes at work in the interstellar medium, in particular grain surface chemistry, played a major role in the formation of cometary ices. It supports models in which cometary volatiles formed in the interstellar medium and suffered little processing in the Solar Nebula.

Key words: comets: general – comets: individual: C/1995 01 Hale-Bopp – solar system: formation – ISM: molecules – radio lines: solar system

Send offprint requests to: D. Bockelée-Morvan (dominique.bockelee@obspm.fr)

© European Southern Observatory (ESO) 2000

Online publication: January 18, 2000

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