Test data have been taken at the Kitt Peak Vacuum Telescope to investigate linear and circular polarization measurements. First, the quarter waveplate used in the normal 868.8 nm Fe I longitudinal magnetograms was removed from the beam. The half-wave chopping retarders then analyzed linear polarization, and full spectral profiles of the 868.8 nm Fe I line (and surrounding region) were obtained. The figure shows that several lines are observed in a sunspot with strong linear polarization profiles. Maps of the linear polarization signal from the Fe I line also showed significant linear polarization in the region surrounding the sunspot. Although much calibration will be needed to remove polarization cross-talk, and changes to the polarization analyzer will also be needed, these test data suggest that the KPVT could be used to measure the vector magnetic field across the whole solar disk.
Secondly, circular polarization profiles of the chromospheric Ca II 854.2 nm absorption line were measured in two sunspot groups. Magnetograms constructed in the line wing and the line core showed significant structural differences, with the line wing magnetograms resembling the photospheric magnetogram measured in a nearby Fe I line. Work is in progress to understand how the circular polarization profile as it changes through the spectral line can be used to measure the magnetic field at different heights in the solar atmosphere.
Matt Penn, Harry Jones