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Photometric survey of binary near-Earth asteroids |
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| Authors: | P Pravec P Scheirich L Šarounová G Hahn G Esquerdo Z Krzeminski BD Warner MC Nolan LAM Benner A Galád W Holliday YuN Krugly R Whiteley DR DeGraff S Larson WR Cooney Jr J Zhu R Dyvig V Reddy Š Gajdoš G Masi D Higgins B Knight R Behrend G Burki C Demeautis N Waelchli A Klotz M Rieugné V Cotrez G Kober |
| Institution: | a Astronomical Institute, Academy of Sciences of the Czech Republic, Fri?ova 1, CZ-25165 Ond?ejov, Czech Republic b DLR Institute of Planetary Research, Rutherfordstr. 2, D-12489 Berlin, Germany c Department of Physics and Astronomy, University of Western Ontario, London, ON N6A 3K7, Canada d Carbuncle Hill Observatory, P.O. Box 946, Coventry, RI 02816, USA e Palmer Divide Observatory, 17995 Bakers Farm Rd., Colorado Springs, CO 80908, USA f Space Science Institute, 4603 Orange Knoll Ave., La Canada, CA 91011, USA g Arecibo Observatory, National Astronomy and Ionosphere Center, Arecibo, PR 00612, USA h Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA i Department of Astronomy, Cornell University, Ithaca, NY 14853, USA j Modra Observatory, Department of Astronomy, Physics of the Earth, and Meteorology, FMFI UK, Bratislava SK-84248, Slovakia k River Oaks Observatory, 1125 Isaac Creek Circle, New Braunfels, TX 78132, USA l Institute of Astronomy of Kharkiv National University, Sumska Str. 35, Kharkiv 61022, Ukraine m Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA n Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA o Department of Astronomy, University of California, 601 Campbell Hall, Berkeley, CA 94720, USA p Alfred University, 1 Saxon Drive, Alfred, NY 14802, USA q Department of Physics and Astronomy, University of Arkansas at Little Rock, Little Rock, AR 72204, USA r BREC, LSU, BRAS Highland Road Park Observatory, 13800 Highland Rd., Baton Rouge, LA 70810, USA s Santana Observatory, Rancho Cucamonga, CA 91737, USA t Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing, 100012, China u Badlands Observatory, Quinn, SD 57775, USA v MacLean/Tahoe Observatories, Incline Village, NV 89450, USA w Department of Space Studies, University of North Dakota, Grand Forks, ND 58202, USA x Astronomy Department, Smith College, Northampton, MA 01063, USA y Physics Department, University of Rome “Tor Vergata,” Via della Ricerca Scientifica 1, 00133 Rome, Italy z Campo Catino Observatory, Guarcino, I-03016, Italy aa Hunters Hill Observatory, 7 Mawalan Street, Ngunnawal ACT 2913, Canberra, Australia ab Department of Astronomy, Whitin Observatory, Wellesley College, 106 Central Street, Wellesley, MA 02481, USA ac Observatoire de Genève, CH-1290 Sauverny, Switzerland ad Blauvac Observatory, St Estève 84570-Blauvac, France ae Village-Neuf Observatory, 9 rue de Huningue, F-68300 Saint-Louis, France af F.-X. Bagnoud Observatory, CH-3961 St-Luc, Switzerland ag Saint-Caprais, F-81800 Rabastens, France ah Observatoire de Haute Provence, F-04870 Saint-Michel l'observatoire, France ai Saint-Hélène Observatory, 6 route des Tronquats, F-33480 Saint-Hélène, France aj Antibes Observatory, 252 Chemin Spagnon, F-06600 Antibes, France |
| Abstract: | Photometric data on 17 binary near-Earth asteroids (15 of them are certain detections, two are probables) were analysed and characteristic properties of the near-Earth asteroid (NEA) binary population were inferred. We have found that binary systems with a secondary-to-primary mean diameter ratio Ds/Dp?0.18 concentrate among NEAs smaller than 2 km in diameter; the abundance of such binaries decreases significantly among larger NEAs. Secondaries show an upper size limit of Ds=0.5-1 km. Systems with Ds/Dp?0.5 are abundant but larger satellites are significantly less common. Primaries have spheroidal shapes and they rotate rapidly, with periods concentrating between 2.2 to 2.8 h and with a tail of the distribution up to ∼4 h. The fast rotators are close to the critical spin for rubble piles with bulk densities about 2 g/cm3. Orbital periods show an apparent cut-off at Porb∼11 h; closer systems with shorter orbital periods have not been discovered, which is consistent with the Roche limit for strengthless bodies. Secondaries are more elongated on average than primaries. Most, but not all, of their rotations appear to be synchronized with the orbital motion; nonsynchronous secondary rotations may occur especially among wider systems with Porb>20 h. The specific total angular momentum of most of the binary systems is similar to within ±20% and close to the angular momentum of a sphere with the same total mass and density, rotating at the disruption limit; this suggests that the binaries were created by mechanism(s) related to rotation near the critical limit and that they neither gained nor lost significant amounts of angular momentum during or since formation. A comparison with six small asynchronous binaries detected in the main belt of asteroids suggests that the population extends beyond the region of terrestrial planets, but with characteristics shifted to larger sizes and longer periods. The estimated mean proportion of binaries with Ds/Dp?0.18 among NEAs larger than 0.3 km is 15±4%. Among fastest rotating NEAs larger than 0.3 km with periods between 2.2 and 2.8 h, the mean proportion of such binaries is (66+10−12)%. |
| Keywords: | Asteroids Photometry |
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