Polarization of asteroid (387) Aquitania: the newest member of a class of large inversion angle asteroids

TL;DR

This study reports polarimetric observations of asteroids (234) Barbara and (387) Aquitania, confirming their unusual polarization behavior and suggesting a mineralogical link to ancient solar system surfaces.

Contribution

It is the first to identify (387) Aquitania as part of a class of large inversion angle asteroids with mineralogical implications.

Findings

(387) Aquitania exhibits large inversion angle polarization.

Spinel features suggest a mineralogical origin for polarization.

Circular polarization was not detected.

Abstract

We present new imaging polarimetric observations of two Main Belt asteroids, (234) Barbara and (387) Aquitania, taken in the first half of 2008 using the Dual-Beam Imaging Polarimeter on the University of Hawaii 2.2 meter telescope, located on Mauna Kea, Hawaii. Barbara had been previously shown to exhibit a very unusual polarization-phase curve by Cellino, et al. (2006). Our observations confirm this result and add Aquitania to the growing class of large inversion angle objects. Interestingly, these asteroids show spinel features in their IR spectra suggesting a mineralogical origin to the phase angle-dependent polarimetric features. As spinel is associated with calcium-aluminum-rich inclusions and carbonaceous chondrites, these large inversion angle asteroids may represent some of the oldest surfaces in the solar system. Circular as well as linear polarization measurements were obtained but circular polarization was not detected.