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Astron. Astrophys. 348, 1020-1034 (1999)

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Coordinated radio continuum observations of comets Hyakutake and Hale-Bopp from 22 to 860 GHz

W.J. Altenhoff 1, J.H. Bieging 2, B. Butler 3, H.M. Butner 1,4, R. Chini 5, C.G.T. Haslam 1, E. Kreysa 1, R.N. Martin 2,4, R. Mauersberger 2, J. McMullin 3,4,6, D. Muders 1,4, W.L. Peters 2,4, J. Schmidt 1, J.B. Schraml 1, A. Sievers 7, P. Stumpff 1, C. Thum 8, A. von Kap-herr 1, H. Wiesemeyer 8, J.E. Wink 8 and R. Zylka 1,9

1 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany, (wja@mpifr-bonn.mpg.de)
2 Steward Observatory, The University of Arizona, Tucson, AZ 85721, USA
3 National Radio Astronomy Observatory, P.O. Box 0, Socorro, NM 87801, USA
4 Sub-Millimeter Telescope Observatory, University of Arizona, Tucson, AZ 85721, USA
5 Astronomisches Institut der Ruhr-Universität Bochum, Universitätsstrasse 150/NA 7, D-44780 Bochum, Germany
6 National Radio Astronomy Observatory, P.O. Box 2, Green Bank, WV 24944, USA
7 Instituto de Radioastronomia Millimetrica (IRAM), Avenida Divina Pastora 7 Nucleo Central, E-18012 Granada, Spain
8 Institut de Radio Astronomie Millimétrique, F-38406 St. Martin d'Hères, France
9 Institut für Theoretische Astrophysik (ITA), Universität Heidelberg, Tiergartenstrasse 15, D-69121 Heidelberg, Germany

Received 10 February 1999 / Accepted 28 June 1999

Abstract

We have observed both Comets Hyakutake and Hale-Bopp close to perigee with several telescopes at frequencies between 30 and 860 GHz for an extended period of time. The observed "light" curves can be described as a simple function of heliocentric and geocentric distances without any outburst or noticeable variability with time.

Our most sensitive diameter estimate for C/Hyakutake resulted in an upper limit of 2.1 km. The nuclear diameter of C/Hale-Bopp was determined to 44.2 km after separation from the halo emission.

The central part of both halos can be represented by a Gaussian with a linear size at half power points of 1870 and 11080 km for Hyakutake and Hale-Bopp, respectively. The spectral index for both comets is [FORMULA] = 2.8, indicating a similar particle size distributions in the halo of these comets. For Hale-Bopp the extended emission could be traced to more than [FORMULA] km from its nucleus.

The derived masses, contained in the halo depend strongly on the assumed physical properties of the halo particles. With [FORMULA](1mm) = 75 cm2/g, possibly more appropriate for comets, a halo mass of [FORMULA] g is derived for Hyakutake and of [FORMULA] g for Hale-Bopp.

Key words: radiation mechanisms: thermal – comets: general – comets: individual: C/Hyakutake – comets: individual: Hale-Bopp – radio continuum: ISM

Send offprint requests to: W.J. Altenhoff

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© European Southern Observatory (ESO) 1999

Online publication: August 13, 199
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