The non-convex shape of (234) Barbara, the first Barbarian*

Tanga, P.; Carry, B.; Colas, F.; Delbò, M.; Matter, A.; Hanuš, Josef; Lagoa, V. Alí; Andrei, A. H.; Assafin, M.; Audejean, M.; Behrend, R.; Camargo, J. I. B.; Carbognani, A.; Reyes, M.; Conjat, M.; Cornero, N.; Coward, D.; Crippa, R.; Fantin, E. de Ferra; Devogèle, Maxime; Dubos, G.; Frappa, Eric; Gillon, M.; Hamanowa, Hiroko; Jehin, Emmanuël; Klotz, A.; Kryszczyńska, A.; Lecacheux, J.; Leroy, A.; Manfroid, Jean; Manzini, F.; Maquet, Lucie; Morelle, Etienne; Mottola, S.; Polińska, M.; Roy, R.; Todd, Michael; Vachier, F.; Hernandez, Christian; Wiggins, P.

doi:10.1093/mnras/stv229

Cited by 13 publications

(7 citation statements)

References 40 publications

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“…Barbara itself, in particular, has been extensively studied and was actually found to have a fairly irregular shape including large-scale concavities. The rotation period was also found to be unusually long (P = 26.4744 ± 0.0001 h) (Tanga et al, 2015) compared to other asteroids of the same size. Other known Barbarian asteroids also exhibit slow rotation rates.…”

Section: Introductionmentioning

confidence: 68%

New polarimetric and spectroscopic evidence of anomalous enrichment in spinel-bearing calcium-aluminium-rich inclusions among L-type asteroids

Devogèle

Tanga

Cellino

et al. 2018

Icarus

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Asteroids can be classified into several groups based on their spectral reflectance. Among these groups, the one belonging to the L-class in the taxonomic classification based on visible and near-infrared spectra exhibit several peculiar properties. First, their near-infrared spectrum is characterized by a strong absorption band interpreted as the diagnostic of a high content of the FeO bearing spinel mineral. This mineral is one of the main constituents of Calcium-Aluminum-rich Inclusions (CAI) the oldest mineral compounds found in the solar system. In polarimetry, they possess an uncommonly large value of the inversion angle incompatible with all known asteroid belonging to other taxonomical classes. Asteroids found to possess such a high inversion angle are commonly called Barbarians based on the first asteroid on which this property was first identified, (234) Barbara. In this paper we present the results of an extensive campaign of polarimetric and spectroscopic observations of L-class objects. We have derived phase-polarization curves for a sample of 7 Barbarians, finding a variety of inversion angles ranging between 25 and 30 • . Spectral reflectance data exhibit variations in terms of spectral slope and absorption features in the near-infrared. We analyzed these data using a Hapke model to obtain some inferences about the relative abundance of CAI and other mineral compounds. By combining spectroscopic and polarimetric results, we find evidence that the polarimetric inversion angle is directly correlated with the presence of CAI, and the peculiar polarimetric properties of Barbarians are primarily a consequence of their anomalous composition.

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Section: Introductionmentioning

confidence: 68%

New polarimetric and spectroscopic evidence of anomalous enrichment in spinel-bearing calcium-aluminium-rich inclusions among L-type asteroids

Devogèle

Tanga

Cellino

et al. 2018

Icarus

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“…There is a group of newly discovered asteroids called Barbarians after its first member, 234 Barbara, that are thought to be very old according to their polarimetric and spectral properties (Tanga et al 2015). These observations indicate rather high content of calcium-aluminium-rich inclusions (Sunshine et al 2008).…”

Section: Discussionmentioning

confidence: 99%

Slowly increasing elongations of non-spherical asteroids caused by collisions

Henych

Pravec

2015

Mon. Not. R. Astron. Soc.

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Asteroids are frequently colliding with small projectiles. Although each individual small collision is not very important, their cumulative effect can substantially change topography and also the overall shape of an asteroid. We run simulations of random collisions onto a single target asteroid represented by triaxial ellipsoid. We investigated asteroids of several hundred meters to about 18 km in diameter for which we assumed all material excavated by the collision to escape the asteroid. The cumulative effect of these collisions is an increasing elongation of the asteroid figure. However, the estimated timescale of this process is much longer than the collisional lifetime of asteroids. Therefore, we conclude that small collisions are probably not responsible for the overall shape of small asteroids.

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“…Recent algorithms such as KOALA (Carry et al, 2010a(Carry et al, , 2012Kaasalainen et al, 2011) and ADAM (Viikinkoski et al, 2015a) allow simultaneous derivation of the spin, 3D shape, and size of an asteroid (see, e.g., Merline et al, 2013;Tanga et al, 2015;Viikinkoski et al, 2015b;Hanuš et al, 2017). This combined multi-data approach has been validated by comparing the 3D shape model of (21) Lutetia by Carry et al (2010b) with the images returned by the ESA Rosetta mission during its fly-by of the asteroid (see Sierks et al, 2011;Carry et al, 2012).…”

Section: D Shape Volume and Densitymentioning

confidence: 99%

3D shape of asteroid (6) Hebe from VLT/SPHERE imaging: Implications for the origin of ordinary H chondrites

Marsset

Carry

Dumas

et al. 2017

A&A

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Context. The high-angular-resolution capability of the new-generation ground-based adaptive-optics camera SPHERE at ESO VLT allows us to assess, for the very first time, the cratering record of medium-sized (D∼100-200 km) asteroids from the ground, opening the prospect of a new era of investigation of the asteroid belt's collisional history. Aims. We investigate here the collisional history of asteroid (6) Hebe and challenge the idea that Hebe may be the parent body of ordinary H chondrites, the most common type of meteorites found on Earth (∼34% of the falls). Methods. We observed Hebe with SPHERE as part of the science verification of the instrument. Combined with earlier adaptiveoptics images and optical light curves, we model the spin and three-dimensional (3D) shape of Hebe and check the consistency of the derived model against available stellar occultations and thermal measurements. Results. Our 3D shape model fits the images with sub-pixel residuals and the light curves to 0.02 mag. The rotation period (7.274 47 h), spin (ECJ2000 λ,β of 343 • ,+47 • ), and volume-equivalent diameter (193 ± 6 km) are consistent with previous determinations and thermophysical modeling. Hebe's inferred density is 3.48 ± 0.64 g.cm −3 , in agreement with an intact interior based on its H-chondrite composition. Using the 3D shape model to derive the volume of the largest depression (likely impact crater), it appears that the latter is significantly smaller than the total volume of close-by S-type H-chondrite-like asteroid families. Conclusions. Our results imply that (6) Hebe is not the most likely source of H chondrites. Over the coming years, our team will collect similar high-precision shape measurements with VLT/SPHERE for ∼40 asteroids covering the main compositional classes, thus providing an unprecedented dataset to investigate the origin and collisional evolution of the asteroid belt.

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The non-convex shape of (234) Barbara, the first Barbarian*

Cited by 13 publications

References 40 publications

New polarimetric and spectroscopic evidence of anomalous enrichment in spinel-bearing calcium-aluminium-rich inclusions among L-type asteroids

New polarimetric and spectroscopic evidence of anomalous enrichment in spinel-bearing calcium-aluminium-rich inclusions among L-type asteroids

Slowly increasing elongations of non-spherical asteroids caused by collisions

3D shape of asteroid (6) Hebe from VLT/SPHERE imaging: Implications for the origin of ordinary H chondrites

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