Observations of strongly polarized extragalactic sources

Visual and infrared photometry and polarimetry of 10 BL Lacertae objects are reported. There is evidence for an increase in the degree of polarization with decreasing wavelength from 1.65 microns to 0.36 microns for BL Lac on 1978 October 28-29. The small change of the position angle with wavelength from 2.28 to 0.55 microns found for OI 090.4 is much less than the change reported by other investigators. The sources 0109 + 224 and 0300 + 471 were found to be highly polarized at 0.44 microns. Some physical causes of wavelength-dependent polarization in the visual-infrared region are discussed.

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