Two components of the coronal emission revealed by EUV spectroscopic observations

TL;DR

This study uses EUV spectroscopic observations to identify and characterize a secondary high-speed upflow component in the solar corona, revealing its properties and association with propagating disturbances, which may influence coronal heating.

Contribution

The paper introduces a modified RB asymmetry analysis technique and demonstrates its effectiveness in identifying and characterizing high-speed upflows in the solar corona.

Findings

Secondary component contributes a few percent of total emission

Velocity of secondary component ranges from 50 to 150 km/s

Secondary component is associated with propagating disturbances

Abstract

Recent spectroscopic observations have revealed the ubiquitous presence of blueward asymmetries of emission lines formed in the solar corona and transition region. These asymmetries are most prominent in loop footpoint regions, where a clear correlation of the asymmetry with the Doppler shift and line width determined from the single Gaussian fit is found. Such asymmetries suggest at least two emission components: a primary component accounting for the background emission and a secondary component associated with high-speed upflows. The latter has been proposed to play a vital role in the coronal heating process and there is no agreement on its properties. Here we slightly modify the initially developed technique of Red-Blue (RB) asymmetry analysis and apply it to both artificial spectra and spectra observed by the EUV Imaging Spectrometer onboard Hinode, and demonstrate that the secondary component usually contributes a few percent of the total emission, has a velocity ranging from 50 to 150 km s-1 and a Gaussian width comparable to that of the primary one in loop footpoint regions. The results of the RB asymmetry analysis are then used to guide a double Gaussian fit and we find that the obtained properties of the secondary component are generally consistent with those obtained from the RB asymmetry analysis. Through a comparison of the location, relative intensity, and velocity distribution of the blueward secondary component with the properties of the upward propagating disturbances revealed in simultaneous images from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory, we find a clear association of the secondary component with the propagating disturbances.