Optical polarimetry of x-ray selected BL Lacs 1989

We report on a program to measure and monitor the optical polarizations of 36 x-ray selected BL Lacs. Many of these objects have not been measured previously for optical polarization. Some of these objects are substantially more polarized at B than I, suggestive of dilution of the synchrotron source by a stellar component, but it does not appear that stellar dilution alone can account for the generally lower P (< 10%) of the x-ray BL Lacs compared to radio selected BL Lacs (< 30%). While the optical polarized flux is correlated with 6 cm radio flux, it is not as strongly correlated with x-ray flux.