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 (France)”. Its main purpose is to carry out a polarimetric survey of minor Solar System objects, named CAPS (Calern Asteroid Polarimetric Survey). In this paper, the new Torino Polarimeter (ToPol) and the results of preliminary scientific validation tests are described. 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 instrumental polarization has been found to be stable within a few 10 units. A total of 124 new polarimetric observation of 78 asteroids are presented. In the case of asteroids already observed in the past, the new data are in agreement with available phase-polarization curves with error bars smaller than most previously published data. We present also data for 21 asteroids than were never observed before in polarimetry.