Plasma diagnostics and Alfvén wave heating of solar prominences by multiwavelength observations.

This article quantitatively investigates the heating of solar prominences—cool, dense plasma structures suspended in the solar corona—focusing on the role of Alfvén waves as a heating mechanism. Using multi-line spectroscopic observations of four quiescent prominences in Hα (6563 Å), Hβ (4861 Å), and Ca ii IR (8542 Å) obtained with the Domeless Solar Telescope at Hida Observatory, the study derives plasma parameters such as temperature, non-thermal velocity, electron density, geometrical thickness, and filling factor through line profile fitting and non-local thermodynamic equilibrium (non-LTE) modeling. The results show that the energy flux carried by Alfvén waves, assuming a magnetic field strength of 20 G, is sufficient to compensate for the net radiative losses in most central regions of the prominences, suggesting Alfvén wave heating as a viable energy source. However, in outer prominence regions where Alfvén wave energy flux is insufficient, additional heating mechanisms—such as enthalpy flux from mass inflow—may contribute, while thermal conduction appears negligible. The study highlights the importance of simultaneous plasma and magnetic field diagnostics for a comprehensive understanding of prominence heating.