Coronal Radiation and Helium λ584 Emission in Active Regions

Abstract

Based on EUV observations of eleven sunspot regions obtained with the Coronal Diagnostic Spectrometer, CDS, on SOHO we have studied the spatial distribution, temporal variation and wavelength shift of the He i λ584 line. We find a relatively high spatial correlation between the coronal line Fe xvi λ360 and the He i λ584 line. This points to coronal back-radiation as an important contributor to the formation of the He i line in active regions. However, contribution to the line formation from another source is suggested by the following two findings: First, the red-shifted line profiles of both He i λ584 and the transition region lines tend to be more intense than blue-shifted profiles. Second, the He i λ584 emission changes significantly faster than the coronal line emission.