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New insights on the binary Asteroid 121 Hermione |
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| Authors: | P Descamps F Marchis J Durech AW Harris J Berthier A Peyrot J Greene M Assafin JIB Camargo F Vachier KM Ivarsen MC Nysewander JB Haislip F Colas L Bernasconi P Baudouin S Sposetti |
| Institution: | a Institut de Mécanique Céleste et de Calcul des Éphémérides, Observatoire de Paris, UMR8028 CNRS, 77 av. Denfert-Rochereau, 75014 Paris, France b University of California at Berkeley, Department of Astronomy, 601 Campbell Hall, Berkeley, CA 94720, USA c Astronomical Institute, Charles University in Prague, Faculty of Mathematics and Physics, V Holesovickach 2, 18000 Prague, Czech Republic d University of Tenessee, 306 EPS Building, 1412 Circle Drive, Knoxville, TN 37996, USA e DLR Institute of Planetary Research, Rutherfordstrasse 2, 12489 Berlin, Germany f Department of Mathematics and Statistics, Gustaf Hallstromin katu 2b, P.O. Box 68, FIN-00014 University of Helsinki, Finland g Makes Observatory, 18, rue G. Bizet - Les Makes - 97421 La Rivière, France h Appalachian State University, Department of Physics and Astronomy, 231 CAP Building, Boone, NC 28608, USA i Observatório do Valongo/UFRJ, Ladeira Pedro Antonio 43, 20080-090 Rio de Janeiro, Brazil j Observatório Nacional, Rua General Jose Cristino 77, 20921-400 Rio de Janeiro, Brazil k SETI Institute, 515 N. Whisman Road, Mountain View, CA 94043, USA l University of North Carolina, Chapel Hill, NC 27514, USA m Geneva Observatory, 1290 Sauverny, Switzerland n Observatoire de Paris, LESIA, 5, Place Jules Janssen, 92195 Meudon Cedex, France o Les Engarouines Observatory, 84570 Mallemort-du-Comtat, France p Blauvac Observatory, 84570 St-Estève, France q Harfleur Observatory, 51 Rue Robert Ancel, 76700 Harfleur, France r “Le Florian”, Villa 4, 880 chemin de Ribac-Estagnol, 06600 Antibes, France s Gnosca Observatory, 6525 Gnosca, Switzerland t Stazione Astronomica di Sozzago, 28060 Sozzago, Italy |
| Abstract: | We report on the results of a 6-month photometric study of the main-belt binary C-type Asteroid 121 Hermione, performed during its 2007 opposition. We took advantage of the rare observational opportunity afforded by one of the annual equinoxes of Hermione occurring close to its opposition in June 2007. The equinox provides an edge-on aspect for an Earth-based observer, which is well suited to a thorough study of Hermione’s physical characteristics. The catalog of observations carried out with small telescopes is presented in this work, together with new adaptive optics (AO) imaging obtained between 2005 and 2008 with the Yepun 8-m VLT telescope and the 10-m Keck telescope. The most striking result is confirmation that Hermione is a bifurcated and elongated body, as suggested by Marchis, et al. Marchis, F., Hestroffer, D., Descamps, P., Berthier, J., Laver, C., de Pater, I., 2005. Icarus 178, 450-464]. A new effective diameter of 187 ± 6 km was calculated from the combination of AO, photometric and thermal observations. The new diameter is some 10% smaller than the hitherto accepted radiometric diameter based on IRAS data. The reason for the discrepancy is that IRAS viewed the system almost pole-on. New thermal observations with the Spitzer Space Telescope agree with the diameter derived from AO and lightcurve observations. On the basis of the new AO astrometric observations of the small 32-km diameter satellite we have refined the orbit solution and derived a new value of the bulk density of Hermione of 1.4 + 0.5/−0.2 g cm−3. We infer a macroscopic porosity of ∼33 + 5/−20%. |
| Keywords: | Asteroids rotation surfaces Satellites of Asteroids Eclipses Photometry |
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