The 2000 Rosetta asteroid targets observational campaign: 140 Siwa and 4979 Otawara

¹ DESPA, Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon, France
² Institut d'Astrophysique Spatiale, Bât. 121, Université Paris-Sud, 91405 Orsay, France
³ Osservatorio Astronomico di Torino, 10025 Pino Torinese, Italy
⁴ UFR de Physique Université Denis Diderot -Paris 7, 2 place Jussieu 75005 Paris, France

Corresponding author: A. Le Bras, aurelie.lebras@obspm.fr

Received: 11 July 2001
Accepted: 18 September 2001

Abstract

Photometric and spectroscopic observations of 140 Siwa and 4979 Otawara, targets of the Rosetta mission, have been carried out at the European Southern Observatory (ESO, Chile). The complete lightcurves in V and R of both asteroids and the Siwa spectrum in the range 0.95-2.52 μm have been obtained. We determined the precise synodic rotational period of 140 Siwa (18.495 h ± 0.005 h) and we confirmed the synodic rotational period of 4979 Otawara (2.707 h ± 0.005 h). The phase function has been obtained for both asteroids, allowing the determination of the H_V and G_V parameters: for 4979 Otawara H_V= 14.62 mag, G_V=0.34; for 140 Siwa H_V=8.34 mag, G_V=0.17. The near infrared spectrum of Siwa does not show any spectral feature, which is consistent with a C/P type object.