A Spectroscopic Measurement of High Velocity Spray Plasma from an M-class Flare and Coronal Mass Ejection

TL;DR

This study reports the detection of an exceptionally high Doppler blue-shift in spray plasma from a solar flare, revealing challenges in spectroscopic observations of dynamic solar phenomena and implications for future missions.

Contribution

It presents the first measurement of a 850 km/s Doppler blue-shift in flare-associated plasma using UV/EUV spectroscopy, highlighting observational risks.

Findings

Largest Doppler blue-shift reported in UV/EUV solar spectroscopy.

Large shifts can cause emission lines to appear outside expected wavelength windows.

Implications for spectrometer design and data interpretation in dynamic solar events.

Abstract

Coronal mass ejection spray plasma associated with the M1.5-class flare of 16 February 2011 is found to exhibit a Doppler blue-shift of 850 km/s - the largest value yet reported from ultraviolet (UV) or extreme ultraviolet (EUV) spectroscopy of the solar disk and inner corona. The observation is unusual in that the emission line (Fe XII 193.51 A) is not observed directly, but the Doppler shift is so large that the blue-shifted component appears in a wavelength window at 192.82 A, intended to observe lines of O V, Fe XI and Ca XVII. The Fe XII 195.12 A emission line is used as a proxy for the rest component of 193.51 A. The observation highlights the risks of using narrow wavelength windows for spectrometer observations when observing highly-dynamic solar phenomena. The consequences of large Doppler shifts for ultraviolet solar spectrometers, including the upcoming Multi-slit Solar Explorer (MUSE) mission, are discussed.