Shape and spin determination of Barbarian asteroids^⋆

¹ Université de Liège, Space sciences, Technologies and Astrophysics Research (STAR) Institute, Allée du 6 Août 19c, Sart Tilman, 4000 Liège, Belgium
e-mail: devogele@astro.ulg.ac.be
² Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, 06300 Nice, France
³ Astronomical Institute, Faculty of Mathematics and Physics, Charles University in Prague, 11636 Staré Město, Czech Republic
⁴ CdR & CdL Group: Light-curves of Minor Planets and Variable Stars, Switzerland
⁵ Estación Astrofísica Bosque Alegre, Observatorio Astronómico Córdoba, 5000 BGR Córdoba, Argentina
⁶ Institute of Geology, Adam Mickiewicz University, Krygowskiego 12, 61-606 Poznań, Poland
⁷ Observatoire de Chinon, 37500 Chinon, France
⁸ Geneva Observatory, 1290 Versoix, Switzerland
⁹ Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
¹⁰ Unidad de Astronomía, Fac. de Ciencias Básicas, Universidad de Antofagasta, 02800 Avda. U. de Antofagasta, Antofagasta, Chile
¹¹ Korea Astronomy and Space Science Institute, 776 Daedeokdae-ro, Yuseong-gu, 34055 Daejeon, Republic of Korea
¹² Osservatorio Astronomico della regione autonoma Valle d’Aosta, 11020 Nus AO, Italy
¹³ School of Physics, University of Western Australia, M013, Crawley WA 6009, Australia
¹⁴ Shed of Science Observatory, 5213 Washburn Ave. S, Minneapolis, MN 55410, USA
¹⁵ Akdeniz University, Department of Space Sciences and Technologies, 07058 Antalya, Turkey
¹⁶ TUBITAK National Observatory (TUG), Akdeniz University Campus, 07058 Antalya, Turkey
¹⁷ Department of Physics & Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
¹⁸ Astrophysics Division, Institute of Physics, Jan Kochanowski University, Świ etokrzyska 15, 25-406 Kielce, Poland
¹⁹ Laboratory of Space Researches, Uzhhorod National University, Daleka st., 2a, 88000 Uzhhorod, Ukraine
²⁰ Institute of Physics, Faculty of Natural Sciences, University of P. J. Safarik, Park Angelinum 9, 040 01 Kosice, Slovakia
²¹ Stazione Astronomica di Sozzago, 28060 Sozzago, Italy
²² NaXys, Department of Mathematics, University of Namur, 8 Rempart de la Vierge, 5000 Namur, Belgium
²³ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
²⁴ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
²⁵ Mt. Suhora Observatory, Pedagogical University, Podchora¸żych 2, 30-084 Cracow, Poland
²⁶ Instituto de Astrofísica de Andalucía, CSIC, Apt 3004, 18080 Granada, Spain
²⁷ CITEUC – Centre for Earth and Space Science Research of the University of Coimbra, Observatório Astronómico da Universidade de Coimbra, 3030-004 Coimbra, Portugal
²⁸ Agrupación Astronómica Región de Murcia, 30153 Orihuela, Spain
²⁹ Arroyo Observatory, Arroyo Hurtado, Murcia, Spain
³⁰ 4438 Organ Mesa Loop, Las Cruces, New Mexico 88011, USA

Received: 21 November 2016
Accepted: 21 June 2017

Abstract

Context. The so-called Barbarian asteroids share peculiar, but common polarimetric properties, probably related to both their shape and composition. They are named after (234) Barbara, the first on which such properties were identified. As has been suggested, large scale topographic features could play a role in the polarimetric response, if the shapes of Barbarians are particularly irregular and present a variety of scattering/incidence angles. This idea is supported by the shape of (234) Barbara, that appears to be deeply excavated by wide concave areas revealed by photometry and stellar occultations.

Aims. With these motivations, we started an observation campaign to characterise the shape and rotation properties of Small Main-Belt Asteroid Spectroscopic Survey (SMASS) type L and Ld asteroids. As many of them show long rotation periods, we activated a worldwide network of observers to obtain a dense temporal coverage.

Methods. We used light-curve inversion technique in order to determine the sidereal rotation periods of 15 asteroids and the convergence to a stable shape and pole coordinates for 8 of them. By using available data from occultations, we are able to scale some shapes to an absolute size. We also study the rotation periods of our sample looking for confirmation of the suspected abundance of asteroids with long rotation periods.

Results. Our results show that the shape models of our sample do not seem to have peculiar properties with respect to asteroids with similar size, while an excess of slow rotators is most probably confirmed.