Volume 487, Number 3, September I 2008
|Page(s)||1171 - 1178|
|Section||Planets and planetary systems|
|Published online||01 July 2008|
Asteroid 2867 Steins*
I. Photometric properties from OSIRIS/Rosetta and ground-based visible observations
Laboratoire d'Astrophysique de Marseille, UMR6110 CNRS/Université de Provence, Technopôle de Marseille-Etoile, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France e-mail: email@example.com
2 Jet Propulsion Laboratory, 4800 Oak Grove Drive, MS 183-301, Pasadena, CA 91109, USA
3 LESIA, Observatoire de Paris, 92195 Meudon Principal Cedex, France
4 Université de Paris 7 Denis Diderot, France
5 School of Mathematics and Physics, Queen's University, Belfast, UK
6 Konkoly Observatory, PO Box 67, 1525, Hungary
7 Max-Planck-Institut für Sonnensystemforschung, Germany
Accepted: 25 May 2008
Context. Asteroid 2867 Steins is the first target of the Rosetta space mission with a flyby scheduled in September 2008.
Aims. An early characterization is needed to optimize the flyby parameters and the science operations and to maximize the scientific return. The aim of this article is to characterize the photometric properties of this asteroid.
Methods. The asteroid was imaged with the Narrow Angle Camera (NAC) of the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) during the cruise phase of the Rosetta spacecraft, at a phase angle of significantly larger than achievable from Earth. It was continuously monitored over ~24 h (on 11 March 2006), thus covering four rotational periods, at a temporal cadence of 6 min. An accurate photometric calibration was obtained from the observations of a solar analog star, 16 Cyg B.
Results. The light curve in the R photometric band of the Johnson-Kron-Cousins system has a mean value ± 0.03 and an amplitude of 0.25 ± 0.04 mag. The periodicity was analyzed with different techniques yielding a mean value of the synodic rotational period of 6.054 ± 0.003 h. By combining with ground-based observations obtained at different phase angles, the phase function is constructed and characterized by a linear part having a phase coefficient ± 0.001 mag/deg and a mean value ± 0.04. In terms of the formalism, the best fit photometric values are ± 0.05 and ± 0.07, but the resulting opposition surge of 0.25 mag, although typical of E-type asteroids, is not really constrained because of the lack of data at phase angles below . Altogether the photometric properties of asteroid 2867 Steins (phase function, color and albedo) indicate that it is a somewhat extreme E-type object, although it is known that this quite small population exhibits at least three different surface mineralogies.
Key words: minor planets, asteroids / techniques: photometric
© ESO, 2008
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