Spectral analogues of Barbarian asteroids among CO and CV chondrites

¹ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, 06304 Nice, France
² Institut d’Astrophysique Spatiale, Université Paris-Saclay, CNRS, 91405 Orsay, France
e-mail: max.mahlke@ias.u-psud.fr
³ Université Grenoble Alpes, Institut de Planétologie et d’Astrophysique de Grenoble, CNRS-CNES, 38000 Grenoble, France

Received: 31 January 2023
Accepted: 12 May 2023

Abstract

Context. K- and L-type asteroids are considered to be the parent bodies of CV and CO chondrites. Spectral models of L-types invoke an enrichment in calcium-aluminium-rich inclusions (CAIs) with respect to the chondrites in the meteorite collection. Barbarian asteroids are associated to L-type asteroids yet the relationship between these populations is still not clear.

Aims. We aim to investigate the link between the K- and L-type and Barbarian asteroids and the CV and CO chondrites by means of spectral matching of a large number of reflectance spectra of objects from either population. We seek to identify matches based on observed rather than modelled spectral features.

Methods. We employ a matching criterion that accounts for the residuals and the correlation of the spectral features. The only free parameter in the comparison is the degree of alteration of the asteroids with respect to the meteorites expressed via an exponential model. We derive an absolute scale of similarity between the spectra using laboratory data from irradiation experiments.

Results. CV_OxA chondrites are the best match to the asteroids, in particular to K-type (7 out of 11 asteroids matched) and Barbarians (11 out of 16). CO chondrites provide convincing matches for K-types (5 out of 11) and Barbarians (7 out of 16) as well. A single non-Barbarian L-type is matched to a meteorite. Only a few asteroids are matched to CV_OxB and CV_Red chondrites.

Conclusions. Barbarian asteroids are represented among CO and CV_OxA chondrites without requiring an enrichment of CAIs in the asteroids. Four candidate Barbarian asteroids are identified, three of which are classified as K-types. These asteroids are favourable targets for polarimetric observations. The discrepancy between L-type asteroids and CV and CO chondrites is likely related to the ambiguity of the asteroid class itself. An extension of the taxonomy to include polarimetric properties is required.