Shape and spin determination of Barbarian asteroids

TL;DR

This study characterizes the shapes and rotation periods of Barbarian asteroids, revealing they are generally typical in shape but have a higher prevalence of slow rotators, using light-curve inversion and occultation data.

Contribution

It provides new shape and rotation data for 15 asteroids, confirming the abundance of slow rotators among Barbarian asteroids and applying light-curve inversion techniques.

Findings

Shapes are typical compared to similar-sized asteroids.

An excess of slow rotators among the sample.

Shape models do not show peculiar properties.

Abstract

Context. The so-called Barbarian asteroids share peculiar, but common polarimetric properties, probably related to both their shape and composition. They are named after (234) Barbara, the first on which such properties were identified. As has been suggested, large scale topographic features could play a role in the polarimetric response, if the shapes of Barbarians are particularly irregular and present a variety of scattering/incidence angles. This idea is supported by the shape of (234) Barbara, that appears to be deeply excavated by wide concave areas revealed by photometry and stellar occultations. Aims. With these motivations, we started an observation campaign to characterise the shape and rotation properties of Small Main- Belt Asteroid Spectroscopic Survey (SMASS) type L and Ld asteroids. As many of them show long rotation periods, we activated a worldwide network of observers to obtain a dense temporal coverage. Methods. We used light-curve inversion technique in order to determine the sidereal rotation periods of 15 asteroids and the con- vergence to a stable shape and pole coordinates for 8 of them. By using available data from occultations, we are able to scale some shapes to an absolute size. We also study the rotation periods of our sample looking for confirmation of the suspected abundance of asteroids with long rotation periods. Results. Our results show that the shape models of our sample do not seem to have peculiar properties with respect to asteroids with similar size, while an excess of slow rotators is most probably confirmed.