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

X. Analysis of classical Kuiper belt objects from Herschel^⋆ and Spitzer observations

¹ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, Giessenbachstr., 85741 Garching, Germany
e-mail: vilenius@mpe.mpg.de
² Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly Thege 15-17, 1121 Budapest, Hungary
³ Deutsches Zentrum für Luft- und Raumfahrt e.V., Institute of Planetary Research, Rutherfordstr. 2, 12489 Berlin, Germany
⁴ Northern Arizona University, Department of Physics and Astronomy, PO Box 6010, Flagstaff AZ 86011, USA
⁵ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 - Granada, Spain
⁶ LESIA-Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, France
⁷ Stewart Observatory, The University of Arizona, Tucson AZ 85721, USA
⁸ SRON Netherlands Institute for Space Research, Postbus 800, 9700 AV Groningen, The Netherlands
⁹ UNS-CNRS-Observatoire de la Côte d’Azur, Laboratoire Cassiopée, BP 4229, 06304 Nice Cedex 04, France
¹⁰ Center for Geophysics of the University of Coimbra, Geophysical and Astronomical Observatory of the University of Coimbra, Almas de Freire, 3040-004 Coimbra, Portugal
¹¹ Unidad de Astronomía, Facultad de Ciencias Básicas, Universidad de Antofagasta, 601 avenida Angamos, Antofagasta, Chile
¹² Univ. Paris Diderot, Sorbonne Paris Cité, 4 rue Elsa Morante, 75205 Paris, France
¹³ Laboratoire d’Astrophysique de Marseille, CNRS & Université de Provence, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France

Received: 31 July 2013
Accepted: 19 January 2014

Abstract

Context. The Kuiper belt is formed of planetesimals which failed to grow to planets and its dynamical structure has been affected by Neptune. The classical Kuiper belt contains objects both from a low-inclination, presumably primordial, distribution and from a high-inclination dynamically excited population.

Aims. Based on a sample of classical trans-Neptunian objects (TNOs) with observations at thermal wavelengths we determine radiometric sizes, geometric albedos and thermal beaming factors for each object as well as study sample properties of dynamically hot and cold classicals.

Methods. Observations near the thermal peak of TNOs using infrared space telescopes are combined with optical magnitudes using the radiometric technique with near-Earth asteroid thermal model (NEATM). We have determined three-band flux densities from Herschel/PACS observations at 70.0, 100.0 and 160.0 μm and Spitzer/MIPS at 23.68 and 71.42 μm when available. We use reexamined absolute visual magnitudes from the literature and ground based programs in support of Herschel observations.

Results. We have analysed 18 classical TNOs with previously unpublished data and re-analysed previously published targets with updated data reduction to determine their sizes and geometric albedos as well as beaming factors when data quality allows. We have combined these samples with classical TNOs with radiometric results in the literature for the analysis of sample properties of a total of 44 objects. We find a median geometric albedo for cold classical TNOs of 0.14_-0.07^+0.09 and for dynamically hot classical TNOs, excluding the Haumea family and dwarf planets, 0.085_-0.045^+0.084. We have determined the bulk densities of Borasisi-Pabu (2.1_-1.2^+2.6 g cm^-3), Varda-Ilmarë (1.25_-0.43^+0.40 g cm^-3) and 2001 QC₂₉₈ (1.14_-0.30^+0.34 g cm^-3) as well as updated previous density estimates of four targets. We have determined the slope parameter of the debiased cumulative size distribution of dynamically hot classical TNOs as q = 2.3 ± 0.1 in the diameter range 100 < D < 500 km. For dynamically cold classical TNOs we determine q = 5.1 ± 1.1 in the diameter range 160 < D < 280 km as the cold classical TNOs have a smaller maximum size.