J. Romon

Compositional Surface Diversity in the Trans-Neptunian Objects*

The knowledge of the physical and chemical properties of trans-Neptunian objects (TNOs) is still incomplete and confused. To investigate their physical properties, we are continuing the TNO observational program started in 1997 at ESO in La Silla, Chile with the 3.5 m New Technology Telescope. In February 1999, broadband optical colors were obtained for eight new objects: 1993 FW, 1995 HM5, 1997 CQ29, 1997 CS29, 1997 CT29, 1997 CU29, 1998 FS144, and 1998 WH24. Particular attention has been paid to the observations and data reduction of these faint objects. These new data increase the available statistical sample and will help us to understand the surface properties and the mechanisms of the surface modification of the TNOs. The observed objects present a wide spread of colors. The color distribution does not show any bimodality. Knowledge of the colors of a large number of these objects is important to understand this population, which represents an important reservoir of primordial material.

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

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 (2002) 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 (− 5t o 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.

Searching for water ice on 47171 1999 TC36, 1998 SG35, and 2000 QC243: ESO large program on TNOs and centaurs

Transneptunian objects and Centaurs are supposed to be among the most pristine bodies of the Solar System. To investigate their physical properties and their surface composition, an ESO large program at the Very Large Telescope was carried out. In this paper we present photometric and spectroscopic near-infrared data of two Centaurs (1998 SG35 and 2000 QC243) and one transneptunian object (47171 1999 TC36). For 47171 1999 TC36 and 1998 SG35 visible photometry is also presented. Models of the surface composition of these objects are presented and discussed. By including a small percentage of water ice in our geographical mixtures, we obtain a better agreement with the observations in the H and K bands.

Visible and near-infrared spectroscopy of the Centaur 32532 (2001 PT13). ESO Large Programm on TNOs and Centaurs: First spectroscopy results

We present photometric and spectroscopic data obtained through visible and near-infrared observations of the Centaur 32532 (2001 PT13) performed with FORS1 and ISAAC at the Very Large Telescope (VLT-ESO) within the framework of an ESO large program on the Trans-Neptunian objects (TNOs) and Centaurs. The results show evidence for a difference in the near-infrared spectral behaviour obtained during two observations carried out one month apart. In one spectrum there is the possible presence of signatures of water ice in small amounts. Two models have been proposed to interpret the surface composition of this Centaur.

Unveiling the nature of 10199 Chariklo: near-infrared observations and modeling

Abstract 10199 Chariklo (1997 CU26) is the largest Centaur so far known. We carried out near-infrared observations of this object during two different runs separated by a year. Although no evidence for spectral variations has been found over short time scales, slight differences have been detected between the two observational runs. We interpret these findings as likely due to a heterogeneous composition of the surface of Chariklo. We suggest two different models comprising geographical mixtures of tholins, amorphous carbon, and water ice in slightly different percentages. Our observations confirm the presence of water ice on the surface of this Centaur, as already detected by Brown et al. (1998, Science 280, 1430–1432) and Brown and Koresko (1998, Astrophys. J. 505, L65–67).

Analysis of Trans-Neptunian and Centaur colours: continuous trend or grouping?

We report the results of the rst statistical analysis of colours (B V , V R, V I ,a ndV J) of the Trans-Neptunian and Centaur populations. Using the same statistical techniques applied to dene the current asteroid taxonomy, we nd a continuous spread of the objects between neutral colour to very red. Pushing further the analysis, the TNOs may be split into four groups. The dierences in colour content are interpreted as a consequence of the TNOs evolution (i.e. collisional history, space weathering, ...)

ESO Large Programme on Trans-Neptunian Objects and Centaurs: Spectroscopic Investigation of Centaur 2001 BL41 and TNOs (26181) 1996 GQ21 and (26375) 1999 DE9*

Observational results that are part of an ESO Large Programme dedicated to the characterization of the physical properties of trans-Neptunian objects and Centaurs are presented. We report observations related to the Centaur 2001 BL41 and two trans-Neptunian objects, (26181) 1996 GQ21 and (26375) 1999 DE9. We present results from broadband photometry (JHK filters) and low-dispersion infrared spectroscopy performed with ISAAC at the Very Large Telescope, in Chile. None of the spectra show evidence of absorption features—in particular, water ice features. We use a radiative transfer model to investigate the surface composition of these icy and primitive outer solar system bodies. We suggest models composed of geographical mixtures of organic compounds and minerals.

Photometric and spectroscopic observations of Sycorax, satellite of Uranus

Sycorax is the brightest of the ve irregular Uranian satellites recently discovered. These satellites are supposed to be captured bodies. We present visible and near-infrared photometry, as well as near-infrared spectroscopy of Sycorax. The overall shape of the spectrum is quite puzzling: it has a red slope in the visible (such as Centaurs and Transneptunian objects), whereas the reflectivity strongly decreases beyond 1 ma nd is rather flat over the near-infrared range. We were not able to reproduce the spectral behaviour of Sycorax using simple materials. A rotational eect is suggested to explain the shape of the spectrum. BVRIJ magnitudes have been measured over a period of 1 hour, with ve V measurements which do not show any strong variation. So only a strong change in the magnitude between the V measurements and the J measurement (30 min later) could explain the shape of the spectrum, but further investigation is required to conclude.

Trans-Neptunian Objects

The presence, the physical and dynamical properties, the chemical composition and the possible origin of Trans Neptunians small bodies are reviewd. The enrichment of dust by collisions among TNOs in the Kuiper Belt is also discussed.

Physical studies of KuiperBelt objects: an ESO VLT large program

Since April 2001 a Large Program for the study of physical properties of Trans-Neptunian Objects (TNO) and Centaurs is underway at the Paranal (Very Large Telescope VLT) and La Silla (New Technology Telescope NTT) observatories of the European Southern Observatory (ESO) in Chile. Combining service (SM) and visitor mode (VM) observations multi-wavelength imaging (BVRIJHK filters) and low-dispersion spectroscopy is performed in the visible and near-IR on a sample of objects that should allow a better and more consistent taxonomic characterization and classification of these pristine bodies in our solar system. Starting with a summary of the current knowledge on the Kuiper-Belt and the populations of objects, the paper presents the goals of this project and its scientific and organizational implementation. It illustrates the progress and the scientific achievements by a hynoptic view of results from photometry and spectroscopy of these Solar System objects.