A&A 446, 1177-1184 (2006)
DOI: 10.1051/0004-6361:20053709

Four new binary minor planets: (854) Frostia, (1089) Tama, (1313) Berna, (4492) Debussy

R. Behrend¹, L. Bernasconi^{2, 3}, R. Roy^{2, 4}, A. Klotz^{5, 6}, F. Colas^{7, 2}, P. Antonini^{2, 8}, R. Aoun⁹, K. Augustesen¹⁰, E. Barbotin⁹, N. Berger¹¹, H. Berrouachdi¹², E. Brochard², A. Cazenave⁹, C. Cavadore², J. Coloma¹³, V. Cotrez⁹, S. Deconihout², C. Demeautis², J. Dorseuil¹², G. Dubos⁹, R. Durkee¹⁴, E. Frappa¹⁵, F. Hormuth¹⁶, T. Itkonen¹⁷, C. Jacques¹⁸, L. Kurtze¹⁹, A. Laffont⁹, M. Lavayssière², J. Lecacheux²⁰, A. Leroy⁹, F. Manzini²¹, G. Masi^{22, 23}, D. Matter², R. Michelsen²⁴, J. Nomen²⁵, A. Oksanen²⁶, P. Pääkkönen¹⁷, A. Peyrot¹², E. Pimentel¹⁸, D. Pray²⁷, C. Rinner², S. Sanchez²⁵, K. Sonnenberg²⁸, S. Sposetti²⁹, D. Starkey³⁰, R. Stoss²⁵, J.-P. Teng¹², M. Vignand¹² and N. Waelchli<sup>31

1</sup>  Observatoire de Genève, 1290 Sauverny, Switzerland
    e-mail: Raoul.Behrend@Obs.UniGe.CH
²  Association des Utilisateurs de Détecteurs Électroniques (AUDE), France
³  Observatoire des Engarouines, 84570 Mallemort-du-Comtat, France
⁴  Observatoire de Blauvac, 84570 St-Estève, France
⁵  CESR, Observatoire Midi-Pyrénées, CNRS-UPS, BP 4346, 31028 Toulouse Cedex 04, France
⁶  Observatoire de Haute Provence, 04870 Saint Michel l'Observatoire, France
⁷  IMCCE, 77 avenue Denfert-Rochereau, 75014 Paris, France
⁸  Observatoire de Bédoin, 47 rue Guillaume Puy, 84000 Avignon, France
⁹  Association T60, 14 avenue Édouard Belin, 31400 Toulouse, France
¹⁰  Astronomical Observatory, Copenhagen, Denmark
¹¹  Observatoire de St-Jean de Bournay, 38440 St-Jean de Bournay, France
¹²  Observatoire Les Makes, G. Bizet 18, 97421 La Rivière, France
¹³  Agrupación Astronómica de Sabadell, PO Box 50, 08200 Sabadell, Spain
¹⁴  Shed of Science Observatory, 5213 Washburn Ave S., Minneapolis, MN-55410, USA
¹⁵  Planétarium de Saint-Étienne, 42000 Saint-Étienne, France
¹⁶  Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, 69117 Heidelberg, Germany
¹⁷  Jakokoski Observatory, Univerity of Helsinki, PO Boy 14, 00014 Helsinki, Finland
¹⁸  CEAMIG-REA Observatory, 31545-12 Belo Horizonte, Brazil
¹⁹  Darmstadt University of Technology, Magdalenenstrasse 4, 64289 Darmstadt, Germany
²⁰  Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon, France
²¹  Stazione Astronomica di Sozzago, 28060 Sozzago, Italy
²²  Physics Dept., University of Rome Tor Vergata, Italy
²³  Campo Catino Observatory, 03016 Guarcino, Italy
²⁴  Ørsted DTU, Techn. Univ. of Denmark, Elektrovej, Building 327, 2800 Kgs. Lyngby, Denmark
²⁵  Observatori Astronómico de Mallorca, Camí de l'Observatori, s/n 07144 Costitx, Mallorca, Spain
²⁶  Nyrölä Observatory, Jyväskylän Sirius ry, Kyllikinkatu 1, 40100 Jyväskylä, Finland
²⁷  Carbuncle Hill Observatory, PO Box 946, Coventry, 02816, USA
²⁸  Sternwarte Weinheim, Klingenweg 14, 69469 Weinheim, Germany
²⁹  Observatorio di Gnosca, 6525 Gnosca, Switzerland
³⁰  DeKalb Observatory, 2507 CR 60, Auburn, 46706, USA
³¹  Observatoire François-Xavier Bagnoud, 3961 St-Luc, Switzerland

(Received 28 June 2005 / Accepted 23 September 2005 )

Abstract
Aims.We present evidence that four minor planets of the main belt are binary systems.
Methods.These discoveries are based on CCD photometric measurements made by many observers coordinated in a network of observatories.
Results.Orbital and physical properties are derived from a total of 134 partial light curves involving 26 stations. (854) Frostia, (1089) Tama, (1313) Berna, and (4492) Debussy show mutual eclipses features on their light curves. In all cases, rotation and revolution are synchronous. Synodic periods are 37.728, 16.444, 25.464 and 26.606 h respectively. From a simple model, we have derived their bulk densities as follows: 0.89 0.14, 2.52 0.30, 1.22 0.15 and 0.91 0.10 g cm^-3 respectively. Uncertainties in the bulk densities, arising from scattering and shadow effects are not taken into account. These could increase the density estimates by a factor up to 1.6. Our method of determining bulk density is completely independent of their mass and their diameter estimates. The low rotational periods and the low bulk densities clearly imply a collisional process to explain this kind of binary asteroid. Based on our database of a few thousand light curves of minor planets, the population of similar-sized objects in the main belt is estimated to percent in the 10-50 km diameter class.

Key words: planets and satellites: formation -- minor planets, asteroids -- techniques: photometric

© ESO 2006