On the spectroscopic detection of periodic plasma flows in loops undergoing thermal non-equilibrium

TL;DR

This study investigates the presence of periodic plasma flows in coronal loops undergoing thermal non-equilibrium, using spectroscopic data to detect predicted flows associated with intensity pulsations.

Contribution

It provides the first spectroscopic detection of plasma flows in pulsating coronal loops, confirming some simulation predictions and analyzing detection limitations.

Findings

Detected plasma flows compatible with simulations in some events

Line of sight ambiguities affect detection rates

Instrumental limitations hinder comprehensive detection

Abstract

Context: Long-period intensity pulsations were recently detected in the EUV emission of coronal loops, and have been attributed to cycles of plasma evaporation and condensation driven by thermal non-equilibrium (TNE). Numerical simulations that reproduce this phenomenon also predict the formation of periodic flows of plasma at coronal temperatures along some of the pulsating loops. Aims: In this paper, we aim at detecting these predicted flows of coronal-temperature plasma in pulsating loops. Methods: To this end, we use time series of spatially resolved spectra from the EUV imaging spectrometer (EIS) onboard Hinode, and track the evolution of the Doppler velocity in loops in which intensity pulsations have previously been detected in images of SDO/AIA. Results: We measure signatures of flows that are compatible with the simulations, but only in a fraction of the observed events. We demonstrate that this low detection rate can be explained by line of sight ambiguities, combined with instrumental limitations such as low signal to noise ratio or insufficient cadence.