Analysis of the coronal green line profiles: evidence of excess blueshifts

TL;DR

This study analyzes the coronal green line profiles during a solar eclipse, revealing prevalent blueshifts and multicomponent structures likely related to solar wind and spicules, with implications for coronal heating.

Contribution

It provides the first detailed evidence of excess blueshifts and multicomponent line profiles in the coronal green line during a solar eclipse, highlighting their dependence on solar activity.

Findings

Excess blueshifts observed in line profiles.

Presence of multicomponents with dominant blueshifted features.

Doppler velocities of secondary components range from 20-40 km/s, increasing towards the poles.

Abstract

The coronal green line (Fe XIV 5303 A) profiles were obtained from Fabry-Perot interferometric observations of the solar corona during the total solar eclipse of 21 June 2001 from Lusaka, Zambia. The instrumental width is about 0.2 A and the spectral resolution is about 26000. About 300 line profiles were obtained within a radial range of 1.0-1.5 R\odot and position angle coverage of about 240\circ. The line profiles were fitted with single Gaussian and their intensity, Doppler velocity, and line width have been obtained. Also obtained are the centroids of the line profiles which give a measure of line asymmetry. The histograms of Doppler velocity show excess blueshifts while the centroids reveal a pre-dominant blue wing in the line profiles. It has been found that the centroids and the Doppler velocities are highly correlated. This points to the presence of multiple components in the line profiles with an excess of blueshifted components. We have then obtained the(Blue-Red) wing intensity which clearly reveals the second component, majority of which are blueshifted ones. This confirms that the coronal green line profiles often contain multicomponents with excess blueshifts which also depend on the solar activity. The magnitude of the Doppler velocity of the secondary component is in the range 20-40 km s-1 and they show an increase towards poles. The possible explanations of the multicomponents could be the type II spicules which were recently found to have important to the coronal heating or the nascent solar wind flow, but the cause of the blue asymmetry in the coronal lines above the limb remains unclear.