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Figure of the double Asteroid 90 Antiope from adaptive optics and lightcurve observations
Authors:P Descamps  T Michalowski  F Colas  M Assafin  M Polinska  D Hestroffer  R Vieira-Martins  M Birlan  A Peyrot  J Dorseuil  T Dijoux
Institution:a Institut de Mecanique Céleste et de Calcul des Éphémérides, Observatoire de Paris, 75014 Paris, France
b University of California at Berkeley, Department of Astronomy, 601 Campbell Hall, Berkeley, CA 94720, USA
c Astronomical Observatory, Adam Mickiewicz University, Sloneczna 36, 60-286 Poznan, Poland
d Observatório do Valongo/UFRJ, Universidade Federal do Rio de Janeiro, Rua Ladeira Pedro Antonio, 43, CEP 20080-090 Rio de Janeiro, Brazil
e Rattlesnake Creek Observatory, 16706 Auburn Road, Grass Valley, CA 95949, USA
f UCO/Lick Observatory, Mount Hamilton, CA 95140, USA
g Nicolaus Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warszawa, Poland
h Observatorio Nacional, Rua General José Cristino 77, 20921-400 Rio de Janeiro, Brazil
i Makes Observatory, 18, rue G. Bizet, Les Makes, 97421 La Rivière, La Réunion, France
Abstract:A long-term adaptive optics (AO) campaign of observing the double Asteroid (90) Antiope has been carried out in 2003-2005 using 8-10-m class telescopes, allowing prediction of the circumstances of mutual events occurring during the July 2005 opposition Marchis, F., Descamps, P., Hestroffer, D., Berthier, J., de Pater, I., 2004. Bull. Am. Astron. Soc. 36, 1180]. This is the first opportunity to use complementary lightcurve and AO observations to extensively study the (90) Antiope system, an interesting visualized binary doublet system located in the main belt. The orbital parameters derived from the AO observations have served as input quantities for the derivation of a whole set of other physical parameters (namely shapes, surface scattering, bulk density, and internal properties) from analysis of collected lightcurves. To completely model the observed lightcurves, we employed Roche figures to construct an overall shape solution. The combination of these complementary observations has enabled us to derive a reliable physical and orbital solution for the system. Our model is consistent with a system of slightly non-spherical components, having a size ratio of 0.95 (with Ravg=42.9±0.5 km, separation=171±1 km), and exhibiting equilibrium figures for homogeneous rotating bodies. A comparison with grazing occultation event lightcurves suggests that the real shapes of the components do not depart from Roche equilibrium figures by more than 10%. The J2000 ecliptic coordinates of the pole of the system are λn=200°±2° and αn=38°±2°. The orbital period was refined to P=16.5051±0.0001 h, and the density is found to be slightly lower than previous determinations, with a value of 1.25±0.05 g/cm3, leading to a significant macro-porosity of 30%. Possible scenarios for the origin of the system are also discussed.
Keywords:Satellites of asteroids  Adaptive optics  Asteroids  composition  Asteroids  rotation  Orbit determination  Occultations  Eclipses
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