Physical and dynamical properties of (12929) 1999 TZ1 suggest that it is a Trojan

Free access article

Issue		A&A Volume 483, Number 2, May IV 2008


Page(s)		L17 - L20
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:200809474
Published online		08 April 2008

A&A 483, L17-L20 (2008)
DOI: 10.1051/0004-6361:200809474

Letter

Physical and dynamical properties of (12929) 1999 TZ₁ suggest that it is a Trojan

A. Moullet¹, E. Lellouch¹, A. Doressoundiram¹, J. L. Ortiz², R. Duffard², A. Morbidelli³, P. Vernazza¹, and R. Moreno¹

¹ LESIA-Observatoire de Paris, 5 place J. Janssen, 92195 Meudon, France
e-mail: arielle.moullet@obspm.fr
² CSIC-Instituto de Astrofisíca de Andalusía, Granada, Spain
³ Observatoire de la Côte d'Azur, Nice, France

(Received 28 January 2008 / Accepted 27 March 2008)

Abstract
Context. Small body (12929) 1999 TZ₁ is listed by the Minor Planet Center (MPC) as a Centaur. However, its location close to the Lagrangian point L5 of Jupiter is typical of a Trojan object with large inclination.
Aims. The aim of this work is to provide a global physical and dynamical characterization of this object and to reassess its classification.
Methods. We obtained multi-wavelength observations with IRTF (Hawaii), OSN and IRAM-30 m (Spain), and performed a dynamical simulation of the evolution of its orbital parameters.
Results. Visible photometry monitoring shows a rotation curve with a period (if considered double-peaked) of 10.4 $\pm$ 0.1 h and an absolute R magnitude H_R = 9.792 $\pm$ 0.025. Near-IR spectroscopy indicates a featureless reflectance spectra, with a low spectral slope of 7.2 $\pm$ 0.11%/100 nm. Thermal observations at 250 GHz provide a 4.5 $\sigma$ detection with a flux of 1.22 $\pm$ 0.27 mJy. The combination of the visible and millimeter datasets, assuming a standard thermal model, leads to a geometric albedo p_v = $0.053^{{\rm +0.015}}_{{-0.010}}$ and a mean diameter of 51.5 $\pm$ 5 km.
Conclusions. The low albedo and spectral slope measured are typical of Jupiter's Trojans, but cannot exclude a Centaur nature. However, the dynamical lifetime of the object was estimated to be longer than 1 Gy, which is unlikely for a Centaur and suggests that (12929) 1999 TZ₁ is a Trojan asteroid.

Key words: minor planets, asteroids -- radio continuum: solar system -- infrared: solar system -- celestial mechanics

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