The effects of magnetic-field geometry on longitudinal oscillations of solar prominences: Cross-sectional area variation for thin tubes

TL;DR

This study investigates how variations in magnetic field geometry, specifically cross-sectional area changes in flux tubes, affect the longitudinal oscillations of solar prominences, and finds these effects to be minimal, supporting the pendulum model.

Contribution

The paper introduces a linear perturbation analysis of flux tube configurations to evaluate the impact of cross-sectional area variations on prominence oscillations, confirming the pendulum model's validity.

Findings

Cross-sectional area variations have minimal impact on oscillation properties.

Symmetric and asymmetric expansion factors do not significantly alter oscillation modes.

The pendulum model remains valid despite flux tube geometry variations.

Abstract

Solar prominences are subject to both field-aligned (longitudinal) and transverse oscillatory motions, as evidenced by an increasing number of observations. Large-amplitude longitudinal motions provide valuable information on the geometry of the filament-channel magnetic structure that supports the cool prominence plasma against gravity. Our pendulum model, in which the restoring force is the gravity projected along the dipped field lines of the magnetic structure, best explains these oscillations. However, several factors can influence the longitudinal oscillations, potentially invalidating the pendulum model. The aim of this work is to study the influence of large-scale variations in the magnetic field strength along the field lines, i.e., variations of the cross-sectional area along the flux tubes supporting prominence threads. We studied the normal modes of several flux tube configurations, using linear perturbation analysis, to assess the influence of different geometrical parameters on the oscillation properties. We found that the influence of the symmetric and asymmetric expansion factors on longitudinal oscillations is small.}{We conclude that the longitudinal oscillations are not significantly influenced by variations of the cross-section of the flux tubes, validating the pendulum model in this context.