2 Observations

The observations were obtained during the interval May 1994 - June 1998 with the five channel photopolarimeter of Turin Observatory, attached at the 2.15-m telescope of CASLEO (San Juan, Argentina). The instrument allows simultaneous measurements of polarization in the five bands UBVRI, following the design principles by Piirola (1973, 1988b). The combination of the dichroic beam splitters and the filters cemented to the field lenses of the dichroic filter set matches closely the standard UBVRI system. The final response of the five photomultipliers corresponds to equivalent wavelengths 0.36, 0.43, 0.53, 0.65 and 0.86 $\mu$m.

During each observing run a set of zero and high polarized standards stars were observed to determine both the instrumental polarization and the coordinate transformation into the equatorial system respectively. The net polarization of telescope and instrument, typically $\sim 0.01$ percent, was subtracted from all the data.