Asteroids; dynamics; Satellites of asteroids; Orbit determination
Abstract :
[en] In understanding the composition and internal structure of asteroids, their density is perhaps the most diagnostic quantity. We aim here at characterizing the surface composition, mutual orbit, size, mass, and density of the small main-belt binary asteroid (939) Isberga. For that, we conduct a suite of multi-technique observations, including optical lightcurves over many epochs, near-infrared spectroscopy, and interferometry in the thermal infrared. We develop a simple geometric model of binary systems to analyze the interferometric data in combination with the results of the lightcurve modeling. From spectroscopy, we classify Ibserga as a Sq-type asteroid, consistent with the albedo of 0.14<SUB>-0.06</SUB><SUP>+0.09</SUP> (all uncertainties are reported as 3-σ range) we determine (average albedo of S-types is 0.197 ± 0.153, see Pravec et al. (Pravec et al. [2012]. Icarus 221, 365-387). Lightcurve analysis reveals that the mutual orbit has a period of 26.6304 ± 0.0001 h, is close to circular (eccentricity lower than 0.1), and has pole coordinates within 7° of (225°, +86°) in Ecliptic J2000, implying a low obliquity of 1.5<SUB>-1.5</SUB><SUP>+6.0</SUP> deg . The combined analysis of lightcurves and interferometric data allows us to determine the dimension of the system and we find volume-equivalent diameters of 12.4<SUB>-1.2</SUB><SUP>+2.5</SUP> km and 3.6<SUB>-0.3</SUB><SUP>+0.7</SUP> km for Isberga and its satellite, circling each other on a 33 km wide orbit. Their density is assumed equal and found to be 2.91<SUB>-2.01</SUB><SUP>+1.72</SUP> gcm<SUP>-3</SUP> , lower than that of the associated ordinary chondrite meteorites, suggesting the presence of some macroporosity, but typical of S-types of the same size range (Carry [2012]. Planet. Space Sci. 73, 98-118). The present study is the first direct measurement of the size of a small main-belt binary. Although the interferometric observations of Isberga are at the edge of MIDI capabilities, the method described here is applicable to others suites of instruments (e.g., LBT, ALMA).
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Carry, B.; IMCCE, Observatoire de Paris, UPMC Paris-06, Université Lille1, UMR8028 CNRS, 77 Av. Denfert Rochereau, 75014 Paris, France
Matter, A.; Max Planck institut für Radioastronomie, Auf dem Hügel, 69, 53121 Bonn, Germany
Scheirich, P.; Astronomical Institute, Academy of Sciences of the Czech Republic, Fričova 298, CZ-25165 Ondřejov, Czech Republic
Pravec, P.; Astronomical Institute, Academy of Sciences of the Czech Republic, Fričova 298, CZ-25165 Ondřejov, Czech Republic
Molnar, L.; Department of Physics and Astronomy, Calvin College, 3201 Burton SE, Grand Rapids, MI 49546, USA
Mottola, S.; Deutsches Zentrum für Luft- und Raumfahrt (DLR), 12489 Berlin, Germany
Carbognani, A.; Astronomical Observatory of the Autonomous Region of the Aosta Valley, Loc. Lignan 39, 11020 Nus (Aosta), Italy
Jehin, Emmanuel ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Marciniak, A.; Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
Binzel, R. P.; Department of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
DeMeo, F. E.; Department of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
Birlan, M.; IMCCE, Observatoire de Paris, UPMC Paris-06, Université Lille1, UMR8028 CNRS, 77 Av. Denfert Rochereau, 75014 Paris, France
Delbo, M.; UNS-CNRS-Observatoire de la Côte dAzur, Laboratoire Lagrange, BP 4229 06304 Nice Cedex 04, France
Barbotin, E.; CdR & CdL Group: Lightcurves of Minor Planets and Variable Stars, Switzerland
Behrend, R.; CdR & CdL Group: Lightcurves of Minor Planets and Variable Stars, Switzerland
Bonnardeau, M.; CdR & CdL Group: Lightcurves of Minor Planets and Variable Stars, Switzerland
Colas, F.; IMCCE, Observatoire de Paris, UPMC Paris-06, Université Lille1, UMR8028 CNRS, 77 Av. Denfert Rochereau, 75014 Paris, France
Farissier, P.; Club d'Astronomie de Lyon Ampère (CALA), Place de la Nation, 69120 Vaulx-en-Velin, France
Fauvaud, M.; Observatoire du Bois de Bardon, 16110 Taponnat, France
Fauvaud, S.; Observatoire du Bois de Bardon, 16110 Taponnat, France
Gillier, C.; Club d'Astronomie de Lyon Ampère (CALA), Place de la Nation, 69120 Vaulx-en-Velin, France
Gillon, Michaël ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Origines Cosmologiques et Astrophysiques (OrCa)
Hellmich, S.; Deutsches Zentrum für Luft- und Raumfahrt (DLR), 12489 Berlin, Germany
Hirsch, R.; Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
Leroy, A.; CdR & CdL Group: Lightcurves of Minor Planets and Variable Stars, Switzerland
Manfroid, Jean ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Département d'astrophys., géophysique et océanographie (AGO)
Montier, J.; CdR & CdL Group: Lightcurves of Minor Planets and Variable Stars, Switzerland
Morelle, E.; CdR & CdL Group: Lightcurves of Minor Planets and Variable Stars, Switzerland
Richard, F.; Association T60, 14 Avenue Edouard Belin, 31400 Toulouse, France
Sobkowiak, K.; Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
Strajnic, J.; CdR & CdL Group: Lightcurves of Minor Planets and Variable Stars, Switzerland
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