ESO large program on physical studies of Transneptunian Objects and Centaurs: Visible photometry – First results^*

¹ European Southern Observatory ESO, Alonso de Cordova 3107, Santiago de Chile, Chile
² Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon Cedex, France
³ Astronomical Observatory of Padova, Vicolo dell' Osservatorio 5, 35122 Padova, Italy
⁴ Institute for Astronomy, Universidad Catolica del Norte, Antofagasta, Chile
⁵ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁶ INAF – Observatorio Astronomico di Torino, Strada Osservatorio 20, 10025 Pino Torinese (TO), Italy
⁷ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone (Roma), Italy
⁸ University of Hawaii, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA
⁹ Instituto de Astronomia de Andalucia, PO Box 3004, 18080 Granada, Spain
¹⁰ National Astronomical Observatory, Osawa 2-21-1, Mitaka, Tokyo, Japan
¹¹ Max-Planck-Institut für Aeronomie, Postfach 20, 37189 Katlenburg-Lindau, Germany
¹² Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹³ European Southern Observatory ESO, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany

Corresponding author: H. Boehnhardt, hboehnha@eso.org

Received: 7 May 2002
Accepted: 30 August 2002

Abstract

We present the first results of BVRI photometry of Transneptunian Objects (TNOs) and Centaurs obtained through the ESO Large Program on physical studies of these icy bodies in the outer solar system. In total 28 objects were observed of which 18 are new measurements. Combining our new BVRI photometry with the data summary published by Hainaut & Delsanti ([CITE]) results in a database of 94 objects: 45 Cubewanos, 22 Plutinos, 13 scattered disk objects, 14 Centaurs. The reddening range seems to be similar among the four dynamical classes (-5 to 55%/l00 nm) and only one outlier (1994 ES₂) exists. The spectral gradient distribution of the Cubewanos peaks between 25 to 35%/l00 nm, while for the three other types the maximum seems to fall below 20%/l00 nm. A clustering of red Cubewanos with perihelia beyond ~41 AU in low eccentricity and low inclination orbit suggests that these objects are less affected by the physical processes that potentially produce neutral colors, i.e. resurfacing by collision and by intrinsic activity. For Cubewanos and scattered disk objects, the range of reddening increases with decreasing perihelion distance and with increasing orbital excitation. A correlation of the spectral slope with inclination is present for Cubewanos and scattered disk objects, and is non-existent for the other dynamical types. It is unclear whether these trends (or their absence) are discriminative for the correctness of the resurfacing scenarios. If intrinsic activity is responsible for resurfacing, the start of the effect inside ~41 AU from the Sun may be indicative for the driving agent, while in the collision scenario the survival of the red Cubewano cluster in the central region of the Kuiper-Belt argues for the existence of a population of bodies the surface of which is heavily radiation processed without impact resurfacing.