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Asteroids can be classified into several groups based on their spectralreflectance. Among these groups, the one belonging to the L-class in thetaxonomic classification based on visible and near-infrared spectra exhibitseveral peculiar properties. First, their near-infrared spectrum ischaracterized by a strong absorption band interpreted as the diagnostic of ahigh content of the FeO bearing spinel mineral. This mineral is one of the mainconstituents of Calcium-Aluminum-rich Inclusions (CAI) the oldest mineralcompounds found in the solar system. In polarimetry, they possess an uncommonlylarge value of the inversion angle incompatible with all known asteroidbelonging to other taxonomical classes. Asteroids found to possess such a highinversion angle are commonly called Barbarians based on the first asteroid onwhich this property was first identified, (234)~Barbara. In this paper wepresent the results of an extensive campaign of polarimetric and spectroscopicobservations of L-class objects. We have derived phase-polarization curves fora sample of 7 Barbarians, finding a variety of inversion angles ranging between25 and 30$^{\circ}$. Spectral reflectance data exhibit variations in terms ofspectral slope and absorption features in the near-infrared. We analyzed thesedata using a Hapke model to obtain some inferences about the relative abundanceof CAI and other mineral compounds. By combining spectroscopic and polarimetricresults, we find evidence that the polarimetric inversion angle is directlycorrelated with the presence of CAI, and the peculiar polarimetric propertiesof Barbarians are primarily a consequence of their anomalous composition.

New polarimetric and spectroscopic evidence of anomalous enrichment in spinel-bearing Calcium-Aluminium-rich Inclusions among L-type asteroids