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VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis

P. Vernazza 1, * M. Ferrais 1 L. Jorda 1 J. Hanuš 2 B. Carry 3 M. Marsset 4 M. Brož 5 R. Fetick 1 M. Viikinkoski 6 F. Marchis 7 F. Vachier 8 A. Drouard 1 T. Fusco 1 M. Birlan 8, 9 E. Podlewska-Gaca 10 N. Rambaux 8 M. Neveu 11 P. Bartczak 10 G. Dudziński 10 E. Jehin 12 P. Beck 13 J. Berthier 8 J. Castillo-Rogez 14 F. Cipriani 15 F. Colas 8 C. Dumas 16 J. Ďurech 5 J. Grice 17 M. Kaasalainen 18 A. Kryszczynska 19 P. Lamy 20 H. Le Coroller 1 A. Marciniak 10 T. Michalowski 10 P. Michel 21, 22 T. Santana-Ros 23, 24 P. Tanga 3 A. Vigan 1 O. Witasse 15 B. Yang 25 P. Antonini M. Audejean 26 P. Aurard 27, 28 R. Behrend 29 Z. Benkhaldoun 30 J. M. Bosch A. Chapman L. Dalmon 31 S. Fauvaud 32, 33 Hiroko Hamanowa 34 Hiromi Hamanowa 34 J. His 28, 27 A. Jones 35 D.-H. Kim 36, 37 M.-J. Kim 36 J. Krajewski 10 O. Labrevoir 28, 27 A. Leroy 38 F. Livet 39 D. Molina 40 R. Montaigut J. Oey N. Payre 41 V. Reddy 42 P. Sabin 28, 27 A. G. Sanchez L. Socha
* Corresponding author
Abstract : Context. Until recently, the 3D shape, and therefore density (when combining the volume estimate with available mass estimates), and surface topography of the vast majority of the largest (D  ≥ 100 km) main-belt asteroids have remained poorly constrained. The improved capabilities of the SPHERE/ZIMPOL instrument have opened new doors into ground-based asteroid exploration.Aims. To constrain the formation and evolution of a representative sample of large asteroids, we conducted a high-angular-resolution imaging survey of 42 large main-belt asteroids with VLT/SPHERE/ZIMPOL. Our asteroid sample comprises 39 bodies with D  ≥ 100 km and in particular most D  ≥ 200 km main-belt asteroids (20/23). Furthermore, it nicely reflects the compositional diversity present in the main belt as the sampled bodies belong to the following taxonomic classes: A, B, C, Ch/Cgh, E/M/X, K, P/T, S, and V.Methods. The SPHERE/ZIMPOL images were first used to reconstruct the 3D shape of all targets with both the ADAM and MPCD reconstruction methods. We subsequently performed a detailed shape analysis and constrained the density of each target using available mass estimates including our own mass estimates in the case of multiple systems.Results. The analysis of the reconstructed shapes allowed us to identify two families of objects as a function of their diameters, namely “spherical” and “elongated” bodies. A difference in rotation period appears to be the main origin of this bimodality. In addition, all but one object (216 Kleopatra) are located along the Maclaurin sequence with large volatile-rich bodies being the closest to the latter. Our results further reveal that the primaries of most multiple systems possess a rotation period of shorter than 6 h and an elongated shape (c∕a ≤ 0.65). Densities in our sample range from ~1.3 g cm−3 (87 Sylvia) to ~4.3 g cm−3 (22 Kalliope). Furthermore, the density distribution appears to be strongly bimodal with volatile-poor (ρ ≥ 2.7 g cm−3) and volatile-rich (ρ ≤ 2.2 g cm−3) bodies. Finally, our survey along with previous observations provides evidence in support of the possibility that some C-complex bodies could be intrinsically related to IDP-like P- and D-type asteroids, representing different layers of a same body (C: core; P/D: outer shell). We therefore propose that P/ D-types and some C-types may have the same origin in the primordial trans-Neptunian disk.
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P. Vernazza, M. Ferrais, L. Jorda, J. Hanuš, B. Carry, et al.. VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. Astronomy and Astrophysics - A&A, EDP Sciences, 2021, 654, pp.A56. ⟨10.1051/0004-6361/202141781⟩. ⟨hal-03375585⟩

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