Center to limb variation of penumbral Stokes V profiles

TL;DR

This study analyzes the variation of Stokes V profiles across the penumbra of sunspots to understand the magnetic and flow structures of the Evershed flow, revealing that both vertical and horizontal components are magnetized plasma streams.

Contribution

It provides new insights into the magnetic and flow structure of the Evershed flow by analyzing Stokes V profile variations at different heliocentric angles and velocity classes.

Findings

Presence of additional lobes in Stokes V profiles indicating complex magnetic structures.

The amplitude of lobes increases with blueshift and heliocentric angle.

Profiles show polarity reversal even at disk center for strong redshifts.

Abstract

We investigated the horizontal and the vertical component of the Evershed flow (EF). To this end, we computed average Stokes V profiles for various velocity classes in penumbrae at different heliocentric angles. Our results show that for blueshifted profiles an additional lobe with the same polarity as the spot is present in the blue side of the average Stokes V profile. The amplitude of the additional lobe grows with increasing blueshift and with increasing heliocentric angle. For small redshifts, the profiles show an additional lobe with the opposite polarity as the spot on the red side of the average Stokes V profile. Even at disk center, the original polarity of the average Stokes V profile is reversed for strong redshifts. The transition between the different types of Stokes V profiles is continuous and indicates that not only the vertical, but also the horizontal EF is a magnetized stream of plasma in a magnetic background field.