Letter to the Editor

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

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 ± 0.1 h and an absolute R magnitude H_R = 9.792 ± 0.025. Near-IR spectroscopy indicates a featureless reflectance spectra, with a low spectral slope of 7.2 ± 0.11%/100 nm. Thermal observations at 250 GHz provide a 4.5σ detection with a flux of 1.22 ± 0.27 mJy. The combination of the visible and millimeter datasets, assuming a standard thermal model, leads to a geometric albedo p_v = and a mean diameter of 51.5 ± 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.