Circular Polarization in the DQ Herculis Binary 3A 0729+103

The authors present optical circular polarimetry of the 13th magnitude long-period DQ Her star 3A 0729+103. For the first time, circular polarization has been detected from a member of this class of objects. Observations in the λλ6400 - 8600 spectral region in January and March of 1985 produced results of -0.347±0.067% and -0.236±0.057%, respectively, with an overall result of -0.239±0.030%. No modulation with the rotational period of the white dwarf is seen. Possible polarization mechanisms in the magnetic field of the white dwarf primary star are discussed.