Elemental composition in quiescent prominences

S Parenti,G Del Zanna,J.-C Vial

doi:10.1051/0004-6361/201935147

Abstract

Context. The first ionization potential (FIP) bias is currently used to trace the propagation of solar features ejected by the wind and solar eruptions (coronal mass ejections). The FIP bias also helps us to understand the formation of prominences, as it is a tracer for the solar origin of prominence plasma.Aims. This work aims to provide elemental composition and FIP bias in quiescent solar prominences. This is key information to link these features to remnants of solar eruptions measured in-situ within the heliosphere and to constrain the coronal or photospheric origin of prominence plasma.Methods. We used the differential emission measure technique to derive the FIP bias of two prominences. Quiet Sun chromospheric and transition region data were used to test the atomic data and lines formation processes. We used lines from low stage of ionization of Si, S, Fe, C, N, O, Ni, Mg, and Ne, constraining the FIP bias in the range 4.2 ≤ log T ≤ 5.8. We adopted a density-dependent ionization equilibrium.Results. We showed that the two prominences have photospheric composition. We confirmed a photospheric composition in the quiet Sun. We also identified opacity and/or radiative excitation contributions to the line formation of a few lines regularly observed in prominences.Conclusions. With our results we thus provide important elements for correctly interpreting the upcoming Solar Orbiter/SPICE spectroscopic data and to constrain prominence formation.

Highlights

One of the key open questions about solar prominences is the process(es) of their formation
We investigated the behavior of this doublet and found that the line profiles are Gaussian within the prominence area used for the analysis
We used the DEM technique, which requires us to invert a set of spectral line intensities whose formation temperatures span the relevant range

Summary

Introduction

One of the key open questions about solar prominences is the process(es) of their formation. The two main ideas are the emergence of their magnetic structure from the photoshere, or reorganization of the photospheric and coronal field through reconnections (Parenti 2014; Vial & Engvold 2015). The elemental composition and the first ionization potential (FIP) bias are strongly dependent on this. The FIP bias is present when elements with FIP lower than about 10 eV are enhanced compared to those with higher FIP, with respect to photospheric values. The amplitude of this effect varies depending on the solar region, the temperature and the age of the observed structure (see, e.g., Brooks et al 2015; Laming 2015). For a full review on the subject, see Laming (2015) and Del Zanna & Mason (2018)

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