Reconstruction of a helical prominence in 3D from IRIS spectra and images^⋆

¹ LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris-Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
e-mail: brigitte.schmieder@obspm.fr
² Astronomical Institute, Academy of Sciences of the Czech Republic, Fričova 298, 25165 Ondřejov, Czech Republic
e-mail: maciej.zapior@asu.cas.cz
³ Institut de Recherche en Astrophysique et Planétologie, 31028 Toulouse, France
⁴ SUPA School of Physics and Astronomy, University of Glasgow, Glasgow, G12 8QQ, UK
⁵ Université de Orléans, 45100 Orléans, France

Received: 21 March 2017
Accepted: 14 June 2017

Abstract

Context. Movies of prominences obtained by space instruments e.g. the Solar Optical Telescope (SOT) aboard the Hinode satellite and the Interface Region Imaging Spectrograph (IRIS) with high temporal and spatial resolution revealed the tremendous dynamical nature of prominences. Knots of plasma belonging to prominences appear to travel along both vertical and horizontal thread-like loops, with highly dynamical nature.

Aims. The aim of the paper is to reconstruct the 3D shape of a helical prominence observed over two and a half hours by IRIS.

Methods. From the IRIS Mg ii k spectra we compute Doppler shifts of the plasma inside the prominence and from the slit-jaw images (SJI) we derive the transverse field in the plane of the sky. Finally we obtain the velocity vector field of the knots in 3D.

Results.We reconstruct the real trajectories of nine knots travelling along ellipses.

Conclusions. The spiral-like structure of the prominence observed in the plane of the sky is mainly due to the projection effect of long arches of threads (up to 8 × 10⁴ km). Knots run along more or less horizontal threads with velocities reaching 65 km s^-1. The dominant driving force is the gas pressure.