The Hubble Space Telescope Northern-Hemisphere grid of stellar polarimetric standards

Results are presented from a comprehensive program of optical polarimetry of strongly polarized and null-polarization standard stars. Potential sources of systematic error either instrumental in origin or due to absolute calibration are critically discussed. Although the project emphasized the requirements of a spaceborne optical-UV observatory (HST), the resulting grid of standards represents a distinct improvement over previous such tabulations and offers an opportunity to reference future multiwavelength polarimetry to a common system.