Interstellar circular polarization. II. Northern and southern hemisphere survey results and observational search criteria

Our original survey has been extended to include more northern and southern hemisphere stars; the wavelength coverage was extended and the precision improved for several previously observed stars. Search criteria for interstellar circular polarization based on the linear polarization and reddening have been delineated and refined. Observational data are presented which confirm the theoretical prediction that the wavelength of maximum interstellar linear polarization and the wavelength of the zero crossing of interstellar circular polarization are approximately the same. An intercomparison of the results of various authors is presented and briefly discussed