On the nature of spectral line broadening in solar coronal dimmings

Abstract

We analyze the profiles of iron emission lines observed in solar coronal dimmings associated with coronal mass ejections, using the EUV Imaging Spectrometer on board Hinode. We quantify line profile distortions with empirical coefficients (asymmetry and peakedness) that compare the fitted Gaussian to the data. We find that the apparent line broadenings reported in previous studies are likely to be caused by inhomogeneities of flow velocities along the line of sight, or at scales smaller than the resolution scale, or by velocity fluctuations during the exposure time. The increase in the amplitude of Alfvén waves cannot, alone, explain the observed features. A double-Gaussian fit of the line profiles shows that, both for dimmings and active region loops, one component is nearly at rest while the second component presents a larger Doppler shift than that derived from a single-Gaussian fit.

16 pages, 11 figures - Accepted for publication in ApJ

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• Flows and Non-thermal Velocities in Solar Active Regions Observed with the Extreme-ultraviolet Imaging Spectrometer on Hinode: A Tracer of Active Region Sources of Heliospheric Magnetic Fields?
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• Pre-flare coronal dimmings
• Core and Wing Densities of Asymmetric Coronal Spectral Profiles: Implications for the Mass Supply of the Solar Corona
• On the spectroscopic detection of periodic plasma flows in loops undergoing thermal non-equilibrium
• Remote coronal dimmings related to a circular-ribbon flare
• Stereoscopic Measurements of Coronal Doppler Velocities