Chromospheric polarimetry through multi-line observations of the 850 nm spectral region II: A magnetic flux tube scenario

TL;DR

This study investigates how magnetic flux tube dynamics influence spectral line profiles and polarization signals in the 850 nm region, revealing oscillations, weak linear polarization, and challenges in magnetic field interpretation during magnetic pumping.

Contribution

It provides new insights into the spectral signatures and magnetic field diagnostics of flux tubes during dynamic processes using multi-line chromospheric polarimetry.

Findings

Profiles are periodically dopplershifted with oscillations.

Weak linear polarization signals are detected at flux tube edges.

Magnetic field interpretation is complicated by formation height changes.

Abstract

In this publication we continue the work started in Quintero Noda et al. (2017) examining this time a numerical simulation of a magnetic flux tube concentration. Our goal is to study if the physical phenomena that take place in it, in particular, the magnetic pumping, leaves a specific imprint on the examined spectral lines. We find that the profiles from the interior of the flux tube are periodically dopplershifted following an oscillation pattern that is also reflected in the amplitude of the circular polarization signals. In addition, we analyse the properties of the Stokes profiles at the edges of the flux tube discovering the presence of linear polarization signals for the Ca II lines, although they are weak with an amplitude around 0.5% of the continuum intensity. Finally, we compute the response functions to perturbations in the longitudinal field and we estimate the field strength using the weak field approximation. Our results indicate that the height of formation of the spectral lines changes during the magnetic pumping process which makes the interpretation of the inferred magnetic field strength and its evolution more difficult. These results complement those from previous works demonstrating the capabilities and limitations of the 850 nm spectrum for chromospheric Zeeman polarimetry in a very dynamic and complex atmosphere.