A novel investigation of the small-scale magnetic activity of the quiet Sun via the Hanle effect in the Sr I 4607 \AA\ line

TL;DR

This study uses 3D radiative transfer calculations in a magneto-convection model to investigate the Hanle effect in the Sr I 4607 Å line, revealing insights into small-scale magnetic activity of the quiet Sun and its observable polarization signatures.

Contribution

It introduces a novel approach combining 3D modeling and radiative transfer to analyze the Hanle effect, advancing understanding of quiet Sun magnetic fields and polarization signals.

Findings

Hanle effect depolarizes scattering signals significantly

Predicted polarization variations are detectable with next-generation telescopes

Scattering polarization signals are anti-correlated with continuum intensity

Abstract

One of the key research problems in stellar physics is to decipher the small-scale magnetic activity of the quiet solar atmosphere. Recent magneto-convection simulations that account for small-scale dynamo action have provided three-dimensional (3D) models of the solar photosphere characterized by a high degree of small-scale magnetic activity, similar to that found through theoretical interpretation of the scattering polarization observed in the Sr I 4607 \AA\ line. Here we present the results of a novel investigation of the Hanle effect in this resonance line, based on 3D radiative transfer calculations in a high-resolution magneto-convection model having most of the convection zone magnetized close to the equipartition and a surface mean field strength ${\langle B \rangle}{\approx}170$ G. The Hanle effect produced by the model's magnetic field depolarizes the zero-field scattering polarization signals significantly, to the extent that the center-to-limb variation of the calculated spatially-averaged polarization amplitudes is compatible with the observations. The standard deviation of the horizontal fluctuations of the calculated scattering polarization signals is very sensitive to the model's magnetic field and we find that the predicted spatial variations are sufficiently sizable so as to be able to detect them, especially with the next generation of solar telescopes. We find that at all on-disk positions the theoretical scattering polarization signals are anti-correlated with the continuum intensity. To facilitate reaching new observational breakthroughs, we show how the theoretically predicted polarization signals and spatial variations are modified when deteriorating the signal-to-noise ratio and the spectral and spatial resolutions of the simulated observations.