Characterisation of candidate members of (136108) Haumea’s family^⋆

II. Follow-up observations

¹ European Space Astronomy Centre, ESA, PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
e-mail: benoit.carry@esa.int
² IMCCE, Observatoire de Paris, UPMC, CNRS, 77 Av. Denfert Rochereau, 75014 Paris, France
³ LESIA, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
⁴ Université Paris 7 Denis-Diderot, 5 rue Thomas Mann, 75205 Paris Cedex, France
⁵ Max Planck Institute for Solar System Research, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany
⁶ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago de Chile, Chile
⁷ Queen’s University, Belfast, County Antrim BT7 1NN, UK
⁸ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany

Received: 15 February 2012
Accepted: 16 July 2012

Abstract

Context. From a dynamical analysis of the orbital elements of trans-Neptunian objects (TNOs), Ragozzine & Brown (2007, AJ, 134, 2160) reported a list of candidate members of the first collisional family found among this population, associated with (136 108) Haumea (a.k.a. 2003 EL₆₁).

Aims. We aim to distinguish the true members of the Haumea collisional family from interlopers. We search for water ice on their surfaces, which is a common characteristic of the known family members. The properties of the confirmed family are used to constrain the formation mechanism of Haumea, its satellites, and its family.

Methods. Optical and near-infrared photometry is used to identify water ice. We use in particular the CH₄ filter of the Hawk-I instrument at the European Southern Observatory Very Large Telescope as a short H-band (H_S), the (J − H_S) colour being a sensitive measure of the water ice absorption band at 1.6 μm.

Results. Continuing our previous study headed by Snodgrass, we report colours for 8 candidate family members, including near-infrared colours for 5. We confirm one object as a genuine member of the collisional family (2003 UZ₁₁₇), and reject 5 others. The lack of infrared data for the two remaining objects prevent any conclusion from being drawn. The total number of rejected members is therefore 17. The 11 confirmed members represent only a third of the 36 candidates.

Conclusions. The origin of Haumea’s family is likely to be related to an impact event. However, a scenario explaining all the peculiarities of Haumea itself and its family remains elusive.