AbstractsAstronomy & Space Science

Towards improved diagnostics in terrestrial and solar spectropolarimetry

by Thomas Ryan Swindle

Institution: University of Hawaii – Manoa
Year: 2015
Keywords: polarized sky; aurorae; solar photosphere
Posted: 02/05/2017
Record ID: 2067485
Full text PDF: http://hdl.handle.net/10125/100489


Ph.D. University of Hawaii at Manoa 2014. The dissertation focuses on developing new technologies in sensitive spectropolarimetry, applied to observations of (I) the polarized sky, aurorae, and (II) solar photosphere. In Part I, I demonstrate the need for accurate daytime sky polarization measurements for use in calibrating large aperture telescopes. We have developed an instrument (WAASP) capable of measuring the complete full-sky polarization vector over visible/near-infrared broad bands with a 1% polarimetric sensitivity in the time frame of constant sky illumination patterns. Observations also assist to characterize the background polarization above Haleakal¯a, strongly dependent on such effects as multiple-scattering, aerosols, and timedependent cloud formations. A first analysis of the polarization properties of the local daytime sky are presented. The instrument is also used to measure the full-sky polarization of Earth aurorae, to an extent which had not yet been achieved, demonstrating it as a new tool for potential thermospheric weather diagnostics. Finally, such terrestrial observations allow validation of atomic scattering and high-altitude polarization models. In Part II, I detail an effort to measure the infrared polarized solar spectrum at the limb at the 0.01% level. At this sensitivity, spectropolarimetric signatures appear due to coherent scattering processes in the upper solar atmosphere, but can be difficult to detect due to instrument and seeing-induced polarization crosstalk. We have developed an infrared fiber spectropolarimeter that, coupled with improved guiding on the SOLARC coronagraph, can achieve 1E-4 polarimetric sensitivity for moderate spectral resolution (R=30,000). We employ new techniques that can flat-field and remove residual seeing-induced crosstalk, using the actual data frames. These methods allow, for example, a 1E-4 sensitivity of limb polarization at a wavelength of 1 micron in roughly 15 minute integrations. The theoretical interpretation of certain spectropolarimetric signatures is ongoing, but this demonstrates the potential for exploring scattering polarization in generally cooler portions of the solar photosphere through new line diagnostics. Near the end of Part II, I highlight some of the stronger features of the infrared polarized solar spectrum and comment on their potential applications in diagnosing the solar radiation environment and magnetic field structures.