Broad-band polarization observations of SS 433

The probable identification of SS 433 with the stellar X-ray source A1909 + 04, the likely association of the supernova remnant W50 with this star, the possible interpretation of the X-ray measurements as emission from a highly magnetic white dwarf, and, in general, the unprecedented behavior of SS 433 make this object a candidate for intrinsic polarization of magnetic origin. The paper reports unfiltered visible linear and circular polarization observations of SS 433. The source does not exhibit circular polarization but it does have a somewhat unusual interstellar linear polarization.