“TNOs are Cool”: A survey of the trans-Neptunian region

IV. Size/albedo characterization of 15 scattered disk and detached objects observed with Herschel-PACS^⋆,⋆⋆

¹ LESIA-Observatoire de Paris, CNRS, UPMC Univ. Paris 6, Univ. Paris-Diderot,, 5 place J. Janssen, 92195 Meudon Cedex, France
e-mail: pablo.santos@obspm.fr
² Univ. Paris Diderot, Sorbonne Paris Cité, 4 rue Elsa Morante, 75205 Paris, France
³ Konkoly Observatory of the Hungarian Academy of Sciences, Budapest, Hungary
⁴ Max-Planck-Institut für extraterrestrische Physik (MPE), Garching, Germany
⁵ University of Arizona, Tucson, USA
⁶ Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institute of Planetary Research, Berlin, Germany
⁷ Laboratoire d’Astrophysique de Marseille, CNRS & Université de Provence, Marseille, France
⁸ SRON LEA/HIFI ICC, Postbus 800, 9700 AV Groningen, The Netherlands
⁹ UNS-CNRS-Observatoire de la Côte′Azur, Laboratoire Cassiopée, BP 4229, 06304 Nice Cedex 04, France
¹⁰ Center for Geophysics of the University of Coimbra, Av. Dr. Dias da Silva, 3000-134 Coimbra, Portugal
¹¹ Astronomical Observatory, University of Coimbra, Almas de Freire, 3040-004 Coimbra, Portugal
¹² Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain
¹³ University of Maryland, USA
¹⁴ Space Science and Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK
¹⁵ Max-Planck-Institut für Sonnensystemforschung (MPS), Katlenburg-Lindau, Germany

Received: 28 November 2011
Accepted: 24 January 2012

Abstract

Context. Physical characterization of trans-Neptunian objects, a primitive population of the outer solar system, may provide constraints on their formation and evolution.

Aims. The goal of this work is to characterize a set of 15 scattered disk (SDOs) and detached objects, in terms of their size, albedo, and thermal properties.

Methods. Thermal flux measurements obtained with the Herschel-PACS instrument at 70, 100 and 160 μm, and whenever applicable, with Spitzer-MIPS at 24 and 70 μm, are modeled with radiometric techniques, in order to derive the objects’ individual size, albedo and when possible beaming factor. Error bars are obtained from a Monte-Carlo approach. We look for correlations between these and other physical and orbital parameters.

Results. Diameters obtained for our sample range from 100 to 2400 km, and the geometric albedos (in V band) vary from 3.8% to 84.5%. The unweighted mean V geometric albedo for the whole sample is 11.2% (excluding Eris); 6.9% for the SDOs, and 17.0% for the detached objects (excluding Eris). We obtain new bulk densities for three binary systems: Ceto/Phorcys, Typhon/Echidna and Eris/Dysnomia. Apart from correlations clearly due to observational bias, we find significant correlations between albedo and diameter (more reflective objects being bigger), and between albedo, diameter and perihelion distance (brighter and bigger objects having larger perihelia). We discuss possible explanations for these correlations.