EDP Sciences
Free access
Volume 436, Number 3, June IV 2005
Page(s) 1113 - 1121
Section Planets and planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20042506

A&A 436, 1113-1121 (2005)
DOI: 10.1051/0004-6361:20042506

Analysis of near-IR spectra of 1 Ceres and 4 Vesta, targets of the Dawn mission

P. Vernazza1, T. Mothé-Diniz1, M. A. Barucci1, M. Birlan2, J. M. Carvano1, G. Strazzulla3, M. Fulchignoni1 and A. Migliorini1, 4

1  LESIA, Observatoire de Paris, 92195 Meudon Principal Cedex, France
    e-mail: pierre.vernazza@obspm.fr
2  IMCCE, Observatoire de Paris, 77 Av. Denfert Rochereau, 75014 Paris Cedex, France
3  INAF-Osservatorio Astrofisico di Catania, via Santa Sofia 78, 95123 Catania, Italy
4  Dipartimento di Astronomia di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy

(Received 8 December 2004 / Accepted 3 February 2005)

We obtained high signal to noise spectra of the two targets of the Dawn mission, 4 Vesta and 1 Ceres from observations carried out in remote control between the Observatoire de Paris-Meudon and the NASA Infrared Telescope Facility on Mauna Kea. 4 Vesta was observed in the 0.7-2.5  $\mu{\rm m}$ spectral region at three different rotational phases in order to i) determine the mineral composition; ii) understand the spectral variations across the surface. Vesta was also observed in the 2.0-3.8  $\mu{\rm m}$ range. The 3 $\mu$m absorption feature was not detected, implying the absence of OH and/or H2O-bearing minerals on the asteroid surface at the latitude of our observations. The spectrum of 1 Ceres was obtained in the 2.0-4.1 $\mu$m range and the presence of the 3.06 $\mu$m absorption feature confirmed. Laboratory measurement of ion-irradiated organics and ices suggest that the 3.06 $\mu$m feature can be reproduced with a linear mixture of crystalyne ice and residues of ion-irradiated asphaltite.

Key words: minor planets, asteroids -- techniques: spectroscopic -- infrared: solar system

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© ESO 2005