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

VI. Herschel/PACS observations and thermal modeling of 19 classical Kuiper belt objects^⋆

¹ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, Giessenbachstr., 85741 Garching, Germany
e-mail: vilenius@mpe.mpg.de
² Konkoly Observatory of the Hungarian Academy of Sciences, 1525 Budapest, PO Box 67, Hungary
³ Deutsches Zentrum für Luft- und Raumfahrt e.V., Institute of Planetary Research, Rutherfordstr. 2, 12489 Berlin, Germany
⁴ LESIA-Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, France
⁵ Stewart Observatory, The University of Arizona, Tucson AZ 85721, USA
⁶ SRON LEA/HIFI ICC, Postbus 800, 9700AV Groningen, The Netherlands
⁷ UNS-CNRS-Observatoire de la Côte d’Azur, Laboratoire Cassiopée, BP 4229, 06304 Nice Cedex 04, France
⁸ Center for Geophysics of the University of Coimbra, Av. Dr. Dias da Silva, 3000-134 Coimbra, Portugal
⁹ Astronomical Observatory of the University of Coimbra, Almas de Freire, 3040-04 Coimbra, Portugal
¹⁰ Univ. Paris Diderot, Sorbonne Paris Cité, 4 rue Elsa Morante, 75205 Paris, France
¹¹ Laboratoire d’Astrophysique de Marseille, CNRS & Université de Provence, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
¹² Instituto de Astrofísica de Andalucía (CSIC), Camino Bajo de Huétor 50, 18008 Granada, Spain
¹³ INAF – Osservatorio Astronomico di Roma, via di Frascati, 33, 00040 Monte Porzio Catone, Italy
¹⁴ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
¹⁵ University of Maryland, College Park, MD 20742, USA
¹⁶ IMCCE, Observatoire de Paris, 77 Av. Denfert-Rochereau, 75014 Paris, France
¹⁷ Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Straße 2, 37191 Katlenburg-Lindau, Germany

Received: 25 December 2011
Accepted: 6 March 2012

Abstract

Context. Trans-Neptunian objects (TNO) represent the leftovers of the formation of the solar system. Their physical properties provide constraints to the models of formation and evolution of the various dynamical classes of objects in the outer solar system.

Aims. Based on a sample of 19 classical TNOs we determine radiometric sizes, geometric albedos and beaming parameters. Our sample is composed of both dynamically hot and cold classicals. We study the correlations of diameter and albedo of these two subsamples with each other and with orbital parameters, spectral slopes and colors.

Methods. We have done three-band photometric observations with Herschel/PACS and we use a consistent method for data reduction and aperture photometry of this sample to obtain monochromatic flux densities at 70.0, 100.0 and 160.0  μm. Additionally, we use Spitzer/MIPS flux densities at 23.68 and 71.42  μm when available, and we present new Spitzer flux densities of eight targets. We derive diameters and albedos with the near-Earth asteroid thermal model (NEATM). As auxiliary data we use reexamined absolute visual magnitudes from the literature and data bases, part of which have been obtained by ground based programs in support of our Herschel key program.

Results. We have determined for the first time radiometric sizes and albedos of eight classical TNOs, and refined previous size and albedo estimates or limits of 11 other classicals. The new size estimates of 2002 MS₄ and 120347 Salacia indicate that they are among the 10 largest TNOs known. Our new results confirm the recent findings that there are very diverse albedos among the classical TNOs and that cold classicals possess a high average albedo (0.17 ± 0.04). Diameters of classical TNOs strongly correlate with orbital inclination in our sample. We also determine the bulk densities of six binary TNOs.