Characterization of Solar Telescope Polarization Properties Across the Visible and Near-Infrared Spectrum. Case Study: The Dunn Solar Telescope

摘要

Accurate astrophysical polarimetry requires a proper characterization of thepolarization properties of the telescope and instrumentation employed to obtainthe observations. Determining the telescope and instrument Muller matrix isbecoming increasingly difficult with the increase in aperture size of the newand upcoming solar telescopes. We have carried out a detailed multi-wavelengthcharacterization of the Dunn Solar Telescope (DST) at the National SolarObservatory/Sacramento Peak as a case study and explore various possibilitesfor the determination of its polarimetric properties. We show that thetelescope model proposed in this paper is more suitable than that in previouswork in that it describes better the wavelength dependence of aluminum-coatedmirrors. We explore the adequacy of the degrees of freedom allowed by the modelusing a novel mathematical formalism. Finally, we investigate the use ofpolarimeter calibration data taken at different times of the day tocharacterize the telescope and find that very valuable information on thetelescope properties can be obtained in this manner. The results are alsoconsistent with the entrance window polarizer measurements, opening veryinteresting possibilities for the calibration of future large-aperture solartelescopes such as the ATST or the EST.