Taxonomic classification of asteroids using future Gaia data L. Galluccio (1), P. Bendjoya (1), A. Cellino (2), M. Delbo (1) and P. Tanga(1) (1) Laboratoire Lagrange, UMR7293, Université de Nice Sophia-Antipolis, CNRS, Observatoire de la Côte d’Azur, Bd. de l’Observatoire, 06304 Nice, France, (2) INAF, Astronomical Observatory of Torino, strada Osservatorio 20 10025 Pino Torinese, Italy (laurent.galluccio@oca.eu / Fax:+33 (0)4 92 00 31 21) Abstract The payload of the Gaia space probe includes detec- tors (Blue Photometer: BP and Red Photometer: RP) designed to obtain spectro-photometric data from blue to red (from 330 to 1050 nm). Asteroid data obtained by these detectors will be used to derive reflectance spectra for a number of the order of 100,000 objects [3]. Based on this data-base, it will be possible to de- velop a new asteroid taxonomy. The big advantage of this will be that of including, for the first time after many years, also the blue part of the reflectance spec- trum, which has been essentially lost during the last decades in all the most modern ground-based CCD- based asteroid spectroscopic surveys. The blue part of the reflectance spectrum is essential to discriminate among different sub-classes of the big C-complex, in- cluding the most primitive asteroids which are known to exist. A particular attention will be devoted to the F taxonomic class, which is characterized by interesting polarimetric properties. In order to prepare the algo- rithms needed for building the planned Gaia asteroid taxonomy, a campaign of spectroscopic observations covering the same wavelength interval, and obtained at the same phase angles which will characterize Gaia observations, has been carried out at TNG. The state of the art in these activities will be briefly summarized. 1. Introduction Asteroids are primitive bodies of our Solar System formed around 4.5 billions years ago and very little evolved since then. Thus, the study of these bodies al- lows us scientists to obtain precious information about the processes of formation and evolution of our plane- tary system. Numerous asteroid spectra were collected during these last 20-years, in the visible as in the in- frared wavelengths. These spectra allow us to study the composition of asteroids and various classifications were proposed. The first taxonomies proposed by Zellner et al., Chap- man et al. and Bowell and al. [3] identified three prin- cipal classes: the C class which corresponds to car- bonaceous chondrites, the S class to stony-iron me- teorites and the M class to metallic-iron-nickel mete- orites. Later on, various taxonomies were proposed, built on larger data set and defining more precise classes (Tholen or Bus & Binzel [2]). The payload of Gaia contains two low resolution spectrophotome- ters which will provide spectroscopic observation of around 100,000 asteroids. The taxonomy of all these asteroids will be produced via an unsupervised classi- fication method. 2. Observations A spectroscopic campaign using two dedicated runs at the 3.5 m Telescopio Nazionale Galileo (TNG) at La Palma (Canary islands) has been realized. Thirty four asteroids were measured in the same wavelength in- terval and at the phase angles which will characterize Gaia data. An example of BP-RP relative reflectance derived on the asteroid (720) Bohlinia is shown in Fig.1. The derived reflectance spectra were cloned using a random noising technique but with some constraints guaranteeing that the cloned spectra still are compat- ible with asteroid reflectance spectra. Then the low- resolution spectra produced were normalized at the central wavelength of the Johnson V band (550 nm). 3. Taxonomic classification of TNG spectra The classification of the data set is done via an un- supervised algorithm, which means that no assump- tions are made on the data. The goal is to rely on the data itself without making any use of existing taxo- nomic classifications, which were based on different wavelength intervals and spectral resolution. This ap- EPSC Abstracts Vol. 9, EPSC2014-167, 2014 European Planetary Science Congress 2014 c  Author(s) 2014 E P S C European Planetary Science Congress