DKIST resolves sub-arcsec photospheric scattering polarization

TL;DR

This paper presents the first high-resolution, sub-arcsecond observations of photospheric scattering polarization in the Sr i 4607 Å line, revealing fine-scale structures and advancing diagnostics of solar atmospheric magnetic fields.

Contribution

It provides the first direct, high-resolution maps of photospheric scattering polarization at sub-arcsecond scales using DKIST, demonstrating the telescope's capability to resolve fine polarization structures.

Findings

Detected sub-arcsecond structuring in scattering polarization signals.

Confirmed scattering origin of Sr i 4607 Å polarization through comparison with Fe i line.

Achieved 0.2 arcsecond spatial resolution with 30 s integration.

Abstract

Scattering polarization signals offer a unique diagnostics of the physical conditions in the solar atmosphere, in particular magnetic fields via the Hanle effect. However, their spatial structure remains poorly constrained due to the difficulty of achieving high spatial resolution and polarimetric sensitivity simultaneously. We present the first direct observation of sub-arcsecond structuring in the linear scattering polarization of the photospheric Sr i 4607 \AA\, line near the solar disk center ($\mu$ = 0.74), obtained with the Visible Spectro- Polarimeter (ViSP) at the Daniel K. Inouye Solar Telescope (DKIST). The data achieve about 0".2 resolution with 30 s integration and sufficient sensitivity to detect fine-scale patterns in the total linear polarization, which are evident in Sr i but absent in a nearby Fe i line that is simultaneously observed. Since this Fe i line is more Zeeman-sensitive than the Sr i 4607 \AA\, this disparity confirms that the signals in the Sr i 4607 \AA\, line arise from scattering. These data provide the first spatially resolved two-dimensional maps of photospheric scattering polarization at sub-arcsecond scales, enabled by the capabilities of a 4-meter solar telescope.