Study of an active region prominence using spectropolarimetric data in the He I D₃ multiplet

¹ Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
² Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
³ Consejo Superior de Investigaciones Científicas, Spain
⁴ Istituto ricerche solari Aldo e Cele Daccò (IRSOL), Faculty of Informatics, Università della Svizzera italiana (USI), CH-6605 Locarno, Switzerland

^⋆ Corresponding author; sesteban@iac.es

Received: 30 September 2024
Accepted: 17 January 2025

Abstract

Context. Prominences are cool overdensities of plasma supported by magnetic fields that levitate in the solar corona. The physical characterization of these structures is key for understanding the magnetic field in the corona.

Aims. Our work attempts to shed light on the properties of prominences by using observations at high polarimetric sensitivity in the He I D₃ multiplet taken with the Zürich Imaging Polarimeter-3 instrument at the Istituto ricerche solari Aldo e Cele Daccò.

Methods. We used the Hanle and Zeeman light inversion code to infer the thermodynamic and magnetic properties of an active region prominence, assuming one- and two-component models.

Results. Our observations unveil a great diversity of physical conditions in the prominence. The observed Stokes profiles are usually broad and show interesting features, which can be described assuming a two-component model. The contribution of each component and the trends inferred for some parameters vary with the distance to the solar limb. While both components have analogous properties and contribute similarly close to the limb, a major component mainly describes the properties inferred at 10–40″ away from the limb. Moreover, both components usually show significant differences in thermal broadening, which is essential for ensuring a good fit quality between observations and synthetic profiles. Summarizing, the observed region of the prominence shows line-of-sight velocities of 1–3 km s⁻¹ and rather horizontal fields of 20–80 gauss. We also report hints of a twist close to a prominence foot and changes in the magnetic configuration at specific locations.

Conclusions. Our results indicate a mainly horizontal magnetic field of a few tens of gauss in the prominence. A model of two components with different thermal broadenings and filling factors, depending on the limb distance, is crucial for providing a consistent solution across most of the observed prominence.