Legolas: a modern tool for magnetohydrodynamic spectroscopy

Abstract

Magnetohydrodynamic (MHD) spectroscopy is central to many astrophysical disciplines, ranging from helio- to asteroseismology, over solar coronal (loop) seismology, to the study of waves and instabilities in jets, accretion disks, or solar/stellar atmospheres. MHD spectroscopy quantifies all linear (standing or travelling) wave modes, including overstable (i.e. growing) or damped modes, for a given configuration that achieves force and thermodynamic balance. Here, we present Legolas, a novel, open-source numerical code to calculate the full MHD spectrum of one-dimensional equilibria with flow, that balance pressure gradients, Lorentz forces, centrifugal effects and gravity, enriched with non-adiabatic aspects like radiative losses, thermal conduction and resistivity. The governing equations use Fourier representations in the ignorable coordinates, and the set of linearised equations are discretised using Finite Elements in the important height or radial variation, handling Cartesian and cylindrical geometries using the same implementation. A weak Galerkin formulation results in a generalised (non-Hermitian) matrix eigenvalue problem, and linear algebraic algorithms calculate all eigenvalues and corresponding eigenvectors. We showcase a plethora of well-established results, ranging from p- and g-modes in magnetised, stratified atmospheres, over modes relevant for coronal loop seismology, thermal instabilities and discrete overstable Alfvén modes related to solar prominences, to stability studies for astrophysical jet flows. We encounter (quasi-)Parker, (quasi-)interchange, current-driven and Kelvin-Helmholtz instabilities, as well as non-ideal quasi-modes, resistive tearing modes, up to magneto-thermal instabilities. The use of high resolution sheds new light on previously calculated spectra, revealing interesting spectral regions that have yet to be investigated.

arXiv commentMatches the publication in ApJS, including Erratum

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Cited by in corpus (15)

• The Super-Alfvénic Rotational Instability in accretion disks about black holes
• Magnetohydrodynamic spectroscopy of a non-adiabatic solar atmosphere
• Coronal seismology by slow waves in non-adiabatic conditions
• Legolas 2.0: Improvements and extensions to an MHD spectroscopic framework
• Legolas: magnetohydrodynamic spectroscopy with viscosity and Hall current
• A spectroscopic investigation of thermal instability for cylindrical equilibria with background flow
• The effect of linear background rotational flows on magnetoacoustic modes of a photospheric magnetic flux tube
• Parametric Survey of Nonaxisymmetric Accretion Disk Instabilities: Magnetorotational Instability to Super-Alfvénic Rotational Instability
• Modification of the resistive tearing instability with Joule heating by shear flow
• Safety first: Stability and dissipation of line-tied force-free flux tubes in magnetized coronae
• Neural network classification of eigenmodes in the magnetohydrodynamic spectroscopy code Legolas
• Effect of optically thin cooling curves on condensation formation: Case study using thermal instability
• Acoustic wave properties in footpoints of coronal loops in 3D MHD simulations
• Instabilities in Cylindrical Geometry Using the Minimalist Approach: Formalism and Rotational Instabilities
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