Spectropolarimetric Fluctuations in a Sunspot Chromosphere

TL;DR

This study uses advanced spectropolarimetric observations to analyze fluctuations in a sunspot chromosphere, revealing a link between intensity and circular polarisation that indicates Alfvénic perturbations and enhances understanding of solar magnetic dynamics.

Contribution

It provides new observational evidence of Alfvénic fluctuations in a sunspot chromosphere using state-of-the-art spectropolarimetric data.

Findings

Detected a correlation between intensity and CP fluctuations.

Identified a magnetic field inclination range associated with fluctuations.

Indicated the presence of Alfvénic perturbations in the sunspot.

Abstract

The instrumental advances made in this new era of 4-meter class solar telescopes with unmatched spectropolarimetric accuracy and sensitivity, will enable the study of chromospheric magnetic fields and their dynamics with unprecedented detail. In this regard, spectropolarimetric diagnostics can provide invaluable insight into magneto-hydrodynamic (MHD) wave processes. MHD waves and, in particular, Alfv\'enic fluctuations associated to particular wave modes, were recently recognized as important mechanisms not only for the heating of the outer layers of the Sun's atmosphere and the acceleration of the solar wind, but also for the elemental abundance anomaly observed in the corona of the Sun and other Sun-like stars (also known as first ionisation potential; FIP) effect. Here, we take advantage of state-of-the-art and unique spectropolarimetric IBIS observations to investigate the relation between intensity and circular polarisation (CP) fluctuations in a sunspot chromosphere. Our results show a clear link between the intensity and CP fluctuations in a patch which corresponds to a narrow range of magnetic field inclinations. This suggests the presence of Alfv\'enic perturbations in the sunspot.