The Calern Asteroid Polarimetric Survey using the Torino Polarimeter: assessment of instrument performances and first scientific results

A new polarimeter based on the Wedged double Wollaston concept has been built at the Torino Observatory and installed on a 1-meter telescope at the Calern observing station of the "Observatoire de la Côte d'Azur". Its main purpose is to carry out a polarimetric survey of Solar System objects. This survey is called CAPS (Calern Asteroid Polarimetric Survey). In this paper, the new Torino polarimeter (ToPo) and its preliminary validation campaign is described. The first results of the CAPS survey are also presented. A number of standard stars with known polarization states, as well as a number of asteroids for which the polarimetric properties are known, have been observed in order to assess the instrument accuracy. The instrument response over the field of view and also its stability over single nights and longer periods have also been tested.
It has been found that the instrument polarization is stable within a few $10^{-4}$ units. The first polarimetric observations of a still limited number of asteroids show an excellent agreement with previously available data and make already some significant contributions by adding new data to a number of objects that had been poorly observed so far.