Minor planets and related objects. IX. Photometry and polarimetry of (1685) Toro

UBV photometry, lightcurves, a polarization-phase relation, and rotational polarization curves of Toro were obtained, June-August 1972. The average colors are B - V = 0.87 and U - B = 0.47 mag, showing some reddening with phase. The geometric albedo of Toro in the B filter is 0.14 which corresponds to an effective mean radius of 2.2 km 0.4 (p.e.). The rotational polarization curves indicate that the lightcurves are mostly due to shape, but some albedo variation over the surface is detected as well. The shape is elongated, and probably irregular, with a cross-sectional area ratio of about 3.2, the maximum effective radius is 2.8 km and the minimum, 1.6 km. The rotation is direct with a sidereal period of 10h1 ' j 4'. The rotation axis is at ecliptic longi- tude 200 ` j 20' and 55 `i S `latitude. At optical wavelengths, the surface texture appears to be that of a dusty regolith similar to, but somewhat rougher than that of the Moon.