“TNOs are Cool”: A survey of the trans-Neptunian region - II. The thermal lightcurve of (136108) Haumea (original) (raw)

A&A 518, L147 (2010)

Letter to the Editor

II. The thermal lightcurve of (136108) Haumea

1, C. Kiss2, P. Santos-Sanz1, T. G. Müller3, S. Fornasier1,4, O. Groussin5, P. Lacerda6, J. L. Ortiz7, A. Thirouin7, A. Delsanti1,5, R. Duffard7, A. W. Harris8, F. Henry1, T. Lim9, R. Moreno1, M. Mommert8, M. Mueller10, S. Protopapa11, J. Stansberry12, D. Trilling13, E. Vilenius3, A. Barucci1, J. Crovisier1, A. Doressoundiram1, E. Dotto14, P. J. Gutiérrez7, O. Hainaut15, P. Hartogh11, D. Hestroffer16, J. Horner17, L. Jorda5, M. Kidger18, L. Lara7, M. Rengel11, B. Swinyard9 and N. Thomas19

1 Observatoire de Paris, 5 Place Jules Janssen, 92195 Meudon Cedex, France e-mail: emmanuel.lellouch@obspm.fr
2 Konkoly Observatory of the Hungarian Academy of Sciences, 1525 Budapest, PO Box 67, Hungary
3 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
4 Université Paris-7 “Denis Diderot”, 4 rue Elsa Morante, 75205 Paris Cedex 13, France
5 Laboratoire d'Astrophysique de Marseille, CNRS & Université de Provence, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
6 Newton Fellow of the Royal Society, Astrophysics Research Centre, Physics Building, Queen's University, Belfast, County Antrim, BT7 1NN, UK
7 Instituto de Astrofísica de Andalucía (CSIC) C/ Camino Bajo de Huétor 50, 18008 Granada, Spain
8 Deutsches Zentrum für Luft- und Raumfahrt, Berlin-Adlershof, Rutherfordstraße 2, 12489 Berlin-Adlershof, Germany
9 Space Science and Technology Department, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot, Oxon UK, OX11 0QX, UK
10 Observatoire de la Côte d'Azur, laboratoire Cassiopée BP 4229, 06304 Nice Cedex 4, France
11 Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Straße 2, 37191 Katlenburg-Lindau, Germany
12 Stewart Observatory, The University of Arizona, Tucson AZ 85721, USA
13 Northern Arizona University, Department of Physics & Astronomy, PO Box 6010, Flagstaff, AZ 86011, USA
14 INAF – Osservatorio Astronomico di Roma, via di Frascati, 33, 00040 Monte Porzio Catone, Italy
15 ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei Müchen, Germany
16 IMCCE, Observatoire de Paris, 77 av. Denfert-Rochereau, 75014 Paris, France
17 Department of Physics and Astronomy, Science Laboratories, Durham University, South Road, Durham, DH1 3LE, UK
18 European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino bajo del Castillo, s/n, Urbanizacion Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
19 Universität Bern, Hochschulstrasse 4, 3012 Bern, Switzerland

Received: 31 March 2010
Accepted: 11 May 2010

Abstract

Thermal emission from Kuiper belt object (136108) Haumea was measured with _Herschel_–PACS at 100 _μ_m and 160 _μ_m for almost a full rotation period. Observations clearly indicate a 100 _μ_m thermal lightcurve with an amplitude of a factor of ~2, which is positively correlated with the optical lightcurve. This confirms that both are primarily due to shape effects. A 160 _μ_m lightcurve is marginally detected. Radiometric fits of the mean Herschel- and _Spitzer-_fluxes indicate an equivalent diameter D ~ 1300 km and a geometric albedo p v ~ 0.70–0.75. These values agree with inferences from the optical lightcurve, supporting the hydrostatic equilibrium hypothesis. The large amplitude of the 100 _μ_m lightcurve suggests that the object has a high projected a/b axis ratio (~1.3) and a low thermal inertia as well as possible variable infrared beaming. This may point to fine regolith on the surface, with a lunar-type photometric behavior. The quality of the thermal data is not sufficient to clearly detect the effects of a surface dark spot.

Key words: Kuiper belt objects: individual: (136108) Haumea / techniques: photometric

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Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.