Fine Analysis of 121 Hermione, 45 Eugenia, and 90 Antiope Binary Asteroid Systems With AO Observations
Résumé
We report on a campaign of adaptive optics observations which focuses on 121 Hermione, 45 Eugenia, and 90 Antiope binary asteroids performed with ESO-VLT and Keck II telescopes in 2003-2004. A precessing Keplerian model was used to describe the motion of their companion. The orbital elements are determined accurately using data spanning more than 2 years. The satellite of 121 Hermione revolves at a= 775 /-14 km from the primary in P=2.5714 /-0.001 days with a low eccentricity (e=0.008 /-0.004) and retrograde orbit w.r.t. to the primary's equator (i=175 /-4 deg considering a pole solution (1.9,13.2) deg in ecliptic EQJ2000). The sense of revolution was unambiguously estimated from images separated by a few hours. Keck AO data taken in December 2003 revealed the bi-lobated shape of the primary. The nominal bulk density as derived from observed size of the primary and its 209 km IRAS diameter is 1.2 /-0.3 g/cm3 (Marchis et al., Icarus, 2004). Future observations with better angular resolution will allow us to see if 121 Hermione is a triple system. The orbit of Petit-Prince, moonlet of 45 Eugenia, was constrained using Feb. and Mar. 2004 AO data recorded at the VLT (a=1196 /-4 km, P= 4.7244 /-0.001 days, e=0, i=163 /-6 deg with a pole solution (133 /-3,-40 /-3 deg) in ecliptic B1950), leading to a bulk density of 1.17 g/cm3 considering its 215 km IRAS diameter. Both models predict successfully the positions reported for the discovery of Petit-Prince on Nov. 1998 and of S/2001 (121) 1 by Merline et al. (1999 and 2002). We will also present results on the same-size binary asteroid 90 Antiope, using the same analysis. Feb. and Mar. 2004 VLT-NACO data confirmed that both components are similar (with a Dm 2.4 and a diameter of 110 /-16 km). A preliminary analysis of Feb. and Mar. 2004 VLT data confirms that both components, separated by 170 /-1 km, with a revolution period P=16.5268 - 0.0001h, are quasi-similar (with a Dm ˜ 2.4% and a diameter of 110 /-16 km) leading to a low bulk density of 0.6 /-0.2 g/cm3. NIR colors, shape of the primary, and motions of the apsidal lines of these binaries will be discussed. This work supported by the National Science Foundation Science and Technology Center for Adaptive Optics, is based on observations collected at the European Southern Observatory, Chile and Keck telescope, Hawaii.