A SEARCH FOR POLARIZATION IN DIFFUSE INTERSTELLAR BANDS TOWARD HD-197770

Spectroscopy and spectropolarimetry in the wavelength range 5600-5800 Angstrom have been obtained for the line of sight toward HD 197770, which has a reported polarized 2175 Angstrom extinction bump. The 5780 and 5797 Angstrom diffuse interstellar bands (DIBs) are anomalously weak (by a factor >2) with respect to reddening, whereas the broader 5778 Angstrom band appears to be anomalously strong. None of these bands shows detectable polarization in excess of that in the continuum; aligned classical grains cannot be the carriers of these bands. The ratio of polarization to optical depth in the DIBs is marginally smaller than would be expected if the DIB carriers were the small, presumably carbonaceous, grains responsible for the 2175 Angstrom absorption.