Journal
ASTRONOMY & ASTROPHYSICS
Volume 631, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201834625
Keywords
Sun: corona; techniques: spectroscopic
Categories
Funding
- STFC (UK)
- UK Commonwealth Scholarship Commission via a Rutherford Fellowship
- STFC [ST/P000665/1, ST/J00054X/1, ST/S001042/1, ST/R000743/1] Funding Source: UKRI
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We present an analysis of several Hinode Extreme-ultraviolet Imaging Spectrometer (EIS) observations of coronal line widths in the quiet Sun, up to 1.5 R-circle dot radial distances. Significant variations are found, which indicates no damping of Alfven waves in the quiescent corona. However, the uncertainties in estimating the instrumental width mean that a firm conclusion cannot be reached. We present a discussion of various EIS instrumental issues and suggest that the strongest lines, from Fe XII at 193.5 angstrom and 195.1 angstrom, have anomalous instrumental widths. We also show how line widths in EIS are uncertain when the signal is low, and that the instrumental variation along the slit is also uncertain. We also find an anomalous decrease (up to 40%) in the intensities of these lines in many off-limb and active region observations, and provide evidence that this is due to opacity effects. We find that the most reliable measurements are obtained from the weaker lines.
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