On the widths of the Mg X lines near 60 nm in the corona

Abstract

We examine the line widths of both components of the Mg X 2s ²S_1/2-2p ²P_1/2,3/2 doublet at 60.98 nm and 62.50 nm in the low corona of the quiet Sun, and find that the Doppler width (i.e. half 1/e width) broadens from Δ λ_D ≈ 8.2 pm to ≈9.5 pm (with an estimated relative standard uncertainty of 4%) between the limb and 220 Mm above the limb in the equatorial corona. In a polar coronal hole, the Doppler width increases from 10.8 pm near 30 Mm to 11.4 pm at around 80 Mm. The analysis does not provide any evidence for a narrowing of the emission-line profiles as a function of the distance from the solar limb.