On Lyman-line asymmetries in quiescent prominences

Abstract

Aims. We study the asymmetries of the synthetic hydrogen Lyman lines and the process responsible for their formation.Methods. To obtain the synthetic Lyman line profiles, we use a multi-thread prominence fine-structure model consisting of identical 2D threads. The 2D thread models are in MHS equilibrium, include an empirical prominence-corona transition region, and solve consistently 2D non-LTE radiative transfer. Each thread of the multi-thread model has a randomly assigned line-of-sight (LOS) velocity.Results. The synthetic Lyman spectrum obtained by multi-thread modelling exhibits substantial asymmetries of the line profiles, even though the LOS velocities of individual threads are only of the order of 10 km s-1. Moreover, our results indicate that the synthetic Lyman-α profiles may exhibit an opposite asymmetry to that of the higher Lyman lines.Conclusions. The presence and behaviour of the asymmetrical profiles of the synthetic Lyman lines agree with observed profiles acquired by SUMER. © 2008 ESO.