Stability of thermal modes in cool prominence plasmas

TL;DR

This study analyzes the stability of thermal modes in solar prominence-like plasmas, revealing that thermal instabilities can occur at lower temperatures than previously thought, influencing prominence dynamics.

Contribution

It provides a detailed linear stability analysis of thermal modes considering partial ionization and updated radiative loss functions, highlighting new instability regimes.

Findings

Thermal modes can be unstable at temperatures as low as 15,000 K.

Updated radiative loss functions predict lower temperature thresholds for instability.

Thermal instability may significantly affect prominence evolution.

Abstract

Context: Magnetohydrodynamic thermal modes may play an important role in the formation, plasma condensation, and evolution of solar prominences. Unstable thermal modes due to unbalance between radiative losses and heating can lead to rapid plasma cooling and condensation. An accurate description of the radiative loss function is therefore crucial for this process. Aims: We study the stability of thermal modes in unbounded and uniform plasmas with properties akin to those in solar prominences. Effects due to partial ionization are taken into account. Three different parametrizations of the radiative loss function are used. Methods: By means of a normal mode analysis, we investigate linear nonadiabatic perturbations superimposed on the equilibrium state. We find an approximate instability criterion for thermal modes, while the exact linear growth rate is obtained by numerically solving the general dispersion relation. The stability of thermal disturbances is compared for the three different loss functions considered. Results: Using up-to-date computations of radiative losses derived from the CHIANTI atomic database, we find that thermal modes may be unstable in prominences for lower temperatures than those predicted with previously existing loss functions. Thermal instability can take place for temperatures as low as 15,000 K, approximately. The obtained linear growth rates indicate that this instability might have an important impact on the dynamics and evolution of cool prominence condensations.