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

Abstract

Solar prominences are cool and dense plasma supported by the magnetic field in the solar corona. They are composed of fine-scale structures called threads. Prominences are heated by the incident radiation from the solar atmosphere, but previous studies have shown that additional heating is necessary to maintain the temperature of prominences of about 104 K. This study aims to investigate quantitatively the mechanical heating of the prominences from observations. We performed spectroscopic observations of prominences in Hα (6563 Å), Hβ (4861 Å), and Ca ii IR (8542 Å) with the Domeless Solar Telescope at Hida observatory. The plasma parameters of the prominences are estimated by fittings of line profiles using the single-slab model and by solving the statistical equilibrium equation. By assuming that the turbulent motion is the manifestation of propagating Alfvén waves, net radiative losses and Alfvén wave energy flux in the prominences are estimated from these parameters. As a result, it was found that the energy flux by Alfvén waves is sufficient to compensate for the net radiative losses in most regions of the central part of the prominences. On the other hand, Alfvén wave energy flux tends to be insufficient at the outer part of prominences. In such regions, another heating mechanism such as enthalpy flux of mixing with coronal plasma needs to be considered.