Volume 387, Number 3, June I 2002
|Page(s)||1107 - 1113|
|Section||Celestial mechanics and astrometry|
|Published online||17 May 2002|
VLT observations of comet 46P/Wirtanen*
European Southern Observatory ESO, Alonso de Cordova 3107, PO Box 19001, Santiago 19, Chile e-mail: firstname.lastname@example.org;email@example.com;firstname.lastname@example.org;email@example.com;firstname.lastname@example.org
2 Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 50125 Firenze, Italy e-mail: email@example.com
3 European Southern Observatory ESO, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany e-mail: firstname.lastname@example.org;email@example.com;firstname.lastname@example.org
4 European Space Agency ESA, ESTEC, Keplerlaan, 2200 AG Noordwijk, The Netherlands e-mail: email@example.com;firstname.lastname@example.org
Corresponding author: H. Boehnhardt, email@example.com
Accepted: 28 March 2002
Comet 46P/Wirtanen, prime target of ESA's ROSETTA mission, was successfully observed at the Very Large Telescope Observatory in Chile: on 17 May 1999 with the Test Camera at the Cassegrain focus of the 8.2-m VLT Kueyen telescope and on 8 December 2001 with FORS1 at Unit Telescope 4 Yepun. May 1999: no coma was detected at heliocentric distance AU. From the measured brightness in the Bessell R-filter, a mean nucleus radius of m is derived (for a geometric albedo of 0.04 and a phase darkening of 0.04 mag/deg). The nucleus signal varies during the 2.7 h observing interval and a peak-to-peak amplitude of ~0.38 mag is determined. The measured lightcurve is in agreement with a rotation period of 6–7.5 hours and a ratio of the main nucleus axes of at least 1.4. The non-detection of a coma allows one to put an approximate upper limit for Afρ of <0.45 cm (suggesting a dust production rate of 0.05 kg/s). December 2001: a weak and condensed coma seems to be present in the seeing disk of the comet at 2.9 AU inbound, causing a higher brightness than expected from the previous size estimates of the nucleus. The colour of the comet appears very red ( spectral gradient ~47%/100 nm). The Afρ value of the comet was cm (equivalent to a dust production rate of about 1 kg/s).
Key words: comets: individual: 46P/Wirtanen / comets: general
© ESO, 2002
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