Development of Infrared Instrumentation for High-Resolution and High-Precision Solar Magnetic Field Observations

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The near-infrared part of the solar spectrum between 1 and 2.2 microns is one of the best diagnostic tools for studying solar magnetic fields. At these wavelengths, sets of spectral lines exist that enable precise measurements of the magnetic fields across a large three-dimensional volume of the solar atmosphere, from the photosphere, through the chromosphere, and into the solar corona. This research project would integrate such observations with the high-resolution and high-dynamic-range telescopic capabilities now established at two sites: the National Solar Observatory at Sacramento Peak (NSO/SP) and the Mees Solar Observatory (MSO) of the Institute for Astronomy (IfA) at the University of Hawaii. The aim would be to produce a suite of instruments for precise three-dimensional remote sensing of solar magnetic fields. Study of small-scale magnetic features requires high spatial and time resolution observations over a small field of view (FOV). Measurement of coronal magnetic fields demands high-sensitivity spectropolarimetry over a large FOV, which can be achieved only with reduced spatial and time resolution, given existing coronagraphic capabilities. Two instruments would be developed in this project to meet these broad observational requirements: A Facility IR Spectropolarimeter (FIRS) for the Dunn Solar Telescope (DST) of NSO/SP. This would be a conventional long-slit spectrograph with an innovative multiple-slit design to enhance its efficiency. It would be operated in conjunction with the new high-order adaptive optics (AO) system of the DST, allowing observations of small-scale photospheric magnetic fields, as well as sunspot and active region magnetic fields, over a large FOV with high spatial and moderate time resolution. An IR Imaging Spectropolarimeter (IRIS) based on distributed large-format fiber optics integral field units (IFU). IFU imaging spectroscopy measures the spectra of extended two-dimensional fields without scanning. Combined with an AO system, it can achieve the highest spatial and time resolution possible over a substantial FOV when observing the solar photosphere. On the SOLAR-C coronagraph at MSO, IFU imaging spectroscopy would efficiently map the large-scale coronal magnetic fields with moderate spatial and time resolution.