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Astron. Astrophys. 335, L25-L29 (1998)


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Letter to the Editor

The nucleus and inner coma of Comet 46P/Wirtanen *

P.L. Lamy 1, I. Toth 1, 2, L. Jorda 3, H.A. Weaver 4 and M. A'Hearn 5

1 Laboratoire d'Astronomie Spatiale, B.P. 8, F-13376 Marseille Cedex 12, France (e-mail: lamy@astrsp-mrs.fr)
2 Konkoly Observatory, P.O. Box 67, H-1525 Budapest, Hungary
3 Max-Planck Institut für Aeronomie D-37191 Katlenburg-Lindau, Germany
4 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
5 Department of stronomy, University of Maryland, College Park, MD 20742-2421, USA

Received 21 October 1997 / Accepted 10 March 1998

Abstract

We report the detection of the nucleus of comet 46P/Wirtanen from analysis of images taken with the Planetary Camera (WFPC2) of the Hubble Space Telescope (HST) on 28 August 1996. The high spatial resolution (a WFPC2 pixel projects to 50 km at the distance of the comet) allowed us to separate the signal of the nucleus from that of the coma and to determine the Landolt V and R magnitudes of the nucleus. Assuming a spherical body with a geometric albedo of 0.04 and a phase coefficient of 0.04 mag/deg, we derived a radius of 0.60[FORMULA]0.02 km. The color of the nucleus is moderately red with a gradient of 10% per [FORMULA] at optical wavelengths. From the lightcurve data we derived a rotational period of 6.0[FORMULA]0.3 hr and find that the ratio of the semi-axes of the assumed ellipsoidal body must satisfy [FORMULA]. From an analysis of the dust coma, we derived that [FORMULA] is 23 cm and that the dust production rate is 4 kg sec-1.

Key words: comets: general – comets: individual: 46P/Wirtanen – telescopes: image processing

* Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA contract NAS 5-26555

Send offprint requests to: P.L. Lamy

© European Southern Observatory (ESO) 1998

Online publication: June 18, 1998

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