A&A 450, 1239-1248 (2006)
DOI: 10.1051/0004-6361:20054518

Exploring the surface properties of transneptunian objects and Centaurs with polarimetric FORS1/VLT observations

S. Bagnulo¹, H. Boehnhardt², K. Muinonen³, L. Kolokolova⁴, I. Belskaya⁵ and M. A. Barucci<sup>6

1</sup>  European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile
    e-mail: sbagnulo@eso.org
²  Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany
    e-mail: hboehnha@linmpi.mpg.de
³  Observatory, PO Box 14, 00014 University of Helsinki, Finland
    e-mail: muinonen@cc.helsinki.fi
⁴  University of Maryland, College Park, MD, USA
    e-mail: ludmilla@astro.umd.edu
⁵  Astronomical observatory of Kharkiv National University, 35 Sumska Str., 61022 Kharkiv, Ukraine
    e-mail: irina@astron.kharkov.ua
⁶  LESIA, Observatoire de Paris, 5 place Jules Janssen, 92195 Meudon Cedex, France
    e-mail: antonella.barucci@obspm.fr

(Received 15 November 2005 / Accepted 3 January 2006 )

Abstract
Context.Polarization is a powerful remote-sensing method to investigate solar system bodies. It is an especially sensitive diagnostic tool to reveal physical properties of the bodies whose observational characteristics are governed by small scatterers (dust, regolith surfaces). For these objects, at small phase angles, a negative polarization is observed, i.e., the electric vector  oscillates predominantly in the scattering plane, contrary to what is typical for rather smooth homogeneous surfaces. The behavior of negative polarization with phase angle depends on the size, composition and packing of the scatterers. These characteristics can be unveiled by modelling the light scattering by the dust or regolith in terms of the coherent backscattering mechanism.
Aims.We investigate the surface properties of TNOs and Centaurs by means of polarimetric observations with FORS1 of the ESO VLT.
Methods. We have obtained new broadband polarimetric measurements over a range of phase angles for a TNO, 50000 Quaoar (in the R Bessel filter), and a Centaur, 2060 Chiron (in the Bessel filters). Simultaneously to the polarimetry, we have obtained R broadband photometry for both objects. We have modelled these new observations of Quaoar and Chiron, and revised the modelling of previous observations of the TNO 28978 Ixion using an improved value of its geometric albedo.
Results. TNOs Ixion and Quaoar, and Centaur Chiron show a negative polarization surge. The Centaur Chiron has the deepest polarization minimum (-1.5-1.4%). The two TNOs show differing polarization curves: for Ixion, the negative polarization increases rapidly with phase; for Quaoar, the polarization is relatively small (-0.6%), and nearly constant at the observed phase angles. For all three objects, modelling results suggest that the surface contains an areal mixture of at least two components with different single-scatterer albedos and photon mean-free paths.

Key words: Kuiper Belt -- polarization

SIMBAD Objects

© ESO 2006

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

• If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
• You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
• You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.