New cases of unusual polarimetric behavior in asteroids^*

¹ Complejo Astronómico El Leoncito – CONICET, Av. España 1512 sur, J5402DSP San Juan, Argentina e-mail: rgilhutton@casleo.gov.ar
² Universidad Nacional de San Juan, J. I. de la Roza 590 oeste, 5400 Rivadavia, San Juan, Argentina
³ INAF, Osservatorio Astronomico di Torino, 10025 Pino Torinese (TO), Italy
⁴ Laboratoire Fizeau, UMR 6525 Université Nice Sophia Antipolis , Observatoire de la Côte d'Azur, CNRS, 06108 Nice Cedex 2, France

Received: 30 October 2007
Accepted: 5 February 2008

Abstract

Aims. Results of different polarimetric campaigns at Complejo Astronómico El Leoncito (Casleo), San Juan, Argentina are presented. The aim of these campaigns was to search for objects exhibiting anomalous polarimetric properties, similar to those shown by the Ld-class asteroid (234) Barbara, among members of the same or similar taxonomic classes.

Methods. The data have been obtained with Torino and CASPROF polarimeters at the 2.15 m telescope. The Torino polarimeter is an instrument that allows simultaneous measurement of polarization in five different bands, and CASPROF polarimeter is a two-hole aperture polarimeter with rapid modulation.

Results. The campaigns began in 2005, and we found four new asteroids with Barbara-like polarimetric properties: the L-class objects (172) Baucis, (236) Honoria and (980) Anacostia, and the K-class asteroid (679) Pax. The polarimetric properties of the phase-polarization curves of these objects may be produced by a mixture of high- and low-albedo particles in their regolith as a result of the fragmentation of a substrate that is spectrally analog to the CO3/CV3 chondrites.