Astronomy & Astrophysics manuscript no. 26962_ja c ESO 2021 August 5, 2021 Compositional characterisation of the Themis family M. Marsset1;2, P. Vernazza2, M. Birlan3;4, F. DeMeo5, R. P. Binzel5, C. Dumas1, J. Milli1, and M. Popescu4;3 1 European Southern Observatory (ESO), Alonso de C´ordova 3107, 1900 Casilla Vitacura, Santiago, Chile e-mail:
[email protected] 2 Aix Marseille University, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388, Marseille, France 3 IMCCE, Observatoire de Paris, 77 avenue Denfert-Rochereau, 75014 Paris Cedex, France 4 Astronomical Institute of the Romanian Academy, 5 Cut¸itul de Argint, 040557 Bucharest, Romania 5 Department of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA Received; accepted ABSTRACT Context. It has recently been proposed that the surface composition of icy main-belt asteroids (B-, C-, Cb-, Cg-, P-, and D-types) may be consistent with that of Chondritic porous interplanetary dust particles (CP IDPs). Aims. In the light of this new association, we re-examine the surface composition of a sample of asteroids belonging to the Themis family in order to place new constraints on the formation and evolution of its parent body. Methods. We acquired near-infrared spectral data for 15 members of the Themis family and complemented this dataset with existing spectra in the visible and mid-infrared ranges to perform a thorough analysis of the composition of the family. Assuming end-member minerals and particle sizes (< 2 µm) similar to those found in CP IDPs, we used a radiative transfer code adapted for light scattering by small particles to model the spectral properties of these asteroids.