Spicule emission profiles observed in \ion{He}{i} 10830 \AA

TL;DR

This study uses high-resolution spectropolarimetric observations of extsc{He} I 10830 {A} spicules to analyze their emission profiles and optical thickness variations with height, providing observational constraints for solar chromosphere models.

Contribution

First detailed spectropolarimetric analysis of extsc{He} I 10830 {A} spicule emission profiles with observational data on intensity ratios and their variation with height.

Findings

The blue/red intensity ratio varies with height above the solar limb.

Qualitative agreement between observations and radiative transfer models.

Observational constraints highlight the need for improved chromosphere models.

Abstract

Off-the-limb observations with high spatial and spectral resolution will help us understand the physical properties of spicules in the solar chromosphere Spectropolarimetric observations of spicules in the \ion{He}{i} 10830 \AA\ multiplet were obtained with the Tenerife Infrared Polarimeter on the German Vacuum Tower Telescope at the Observatorio del Teide (Tenerife, Spain). The analysis shows the variation of the off-limb emission profiles as a function of the distance to the visible solar limb. The ratio between the intensities of the blue and the red components of this triplet $({\cal R}=I_{\rm blue}/I_{\rm red})$ is an observational signature of the optical thickness along the light path, which is related to the intensity of the coronal irradiation. We present observations of the intensity profiles of spicules above a quiet Sun region. The observable ${\cal R}$ as a function of the distance to the visible limb is also given. We have compared our observational results to the intensity ratio obtained from detailed radiative transfer calculations in semi-empirical models of the solar atmosphere assuming spherical geometry. The agreement is purely qualitative. We argue that future models of the solar chromosphere and transition region should account for the observational constraints presented here.