Properties of prominence fine-structure threads derived from SOHO/SUMER hydrogen Lyman lines

Abstract

Context: The SOHO/SUMER observations provide us for the first time with the prominence spectra in the Lyman-α line outside the attenuator together with the higher members of the hydrogen Lyman series.
Aims: We derive the prominence fine-structure thread properties by comparing the SOHO/SUMER hydrogen Lyman series observations with the synthetic Lyman lines.
Methods: To obtain the synthetic profiles of the Lyman lines, we used 2D prominence fine-structure thread models with a PCTR and consistently solved the 2D non-LTE multilevel radiative transfer. The trial-and-error method was applied to find the model with the best agreement between the synthetic Lyman line profiles and the observed ones.
Results: The properties of the resulting model with the best match of the synthetic and observed line profiles are central (minimum) temperature T₀ = 7000 K, maximum column mass in the centre of the thread M₀ = 1.1×10^-4 g cm^-2, horizontal field strength in the middle of the thread B_x(0) = 6 Gauss and the boundary pressure p₀ = 0.015 dyn cm^-2.
Conclusions: The Lyman line profiles observed by SOHO/SUMER can be better reproduced by using multi-thread models consisting of a set of the 2D prominence fine-structure threads placed perpendicularly to the line-of-sight, rather than with the single-thread model.