1.5D non-LTE spectral synthesis of a 3D filament and prominence simulation

¹ Centre for mathematical Plasma-Astrophysics, Celestijnenlaan 200B, 3001 Leuven, KU Leuven, Belgium
e-mail: jack.jenkins@kuleuven.be
² SUPA School of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK

Received: 2 September 2022
Accepted: 25 November 2022

Abstract

Context. Overly idealised representations of solar filaments and prominences in numerical simulations have long limited their morphological comparison against observations. Moreover, it is intrinsically difficult to convert simulation quantities into emergent intensity of characteristic, optically thick line cores and/or spectra that are commonly selected for observational study.

Aims. In this paper, we demonstrate how the recently developed Lightweaver framework makes non-‘local thermodynamic equilibrium’ (NLTE) spectral synthesis feasible on a new 3D ab initio magnetohydrodynamic (MHD) filament-prominence simulation, in a post-processing step.

Methods. We clarify the need to introduce filament- and prominent-specific Lightweaver boundary conditions that accurately model incident chromospheric radiation, and include a self-consistent and smoothly varying limb-darkening function.

Results. Progressing from isothermal and isobaric models to the self-consistently generated stratifications within a fully 3D MHD filament-prominence simulation, we find excellent agreement between our 1.5D NLTE Lightweaver synthesis and a popular hydrogen Hα proxy. We computed additional lines including Ca II 8542 alongside the more optically thick Ca II H&K & Mg II h&k lines, for which no comparable proxy exists, and we explore their formation properties within filament and prominence atmospheres.

Conclusions. The versatility of the Lightweaver framework is demonstrated with this extension to 1.5D filament and prominence models, where each vertical column of the instantaneous 3D MHD state is spectrally analysed separately, without accounting for (important) multi-dimensional radiative effects. The general agreement found in the line core contrast of both observations and the Lightweaver-synthesised simulation further validates the current generation of solar filament and prominence models constructed numerically with MPI-AMRVAC.