Choosing emission lines for EIS studies
v2.0, Peter Young
Young
et al. (2007a) discuss the major lines and density
diagnostics
seen in the EIS spectrum. Some of this information is summarised below.
Core lines
Currently there are three core lines that must be in every EIS
study.
These are:
Ca XVII 192.82
Fe XII 195.12
He II 256.32
Transition region lines
The following transition region lines are recommended:
Mg V 276.54
Mg VI 268.99
Mg VII 278.44/280.74
Si VII 275.35
They are all weak lines, but they can become strong in certain
conditions, such as in the footpoints of active region loops. Exposure
times of at least 20 seconds are recommended.
The Mg VII ratio is a density diagnostic. Note that the 278.44 line is
blended with a Si VII line, but the Si VII 275.35 line can be used to
correct this, so make sure this line is also included in your raster.
See Young
et al. (2007b) for more details.
There are a number of weak O IV, V and VI lines throughout the
spectrum. The most useful O V line is at 192.9, lying just next to Ca
XVII 192.82, and so will automatically be in most studies. The best O
VI line is at 184.12.
Coronal lines
Taking a complete set of iron lines is recommended, and the
best
individual lines from each ion are:
Fe VIII 185.21 (warning: blended with Ni XVI line at
high temps.)
Fe IX 197.86
Fe X 184.54
Fe XI 188.23 (actually two Fe XI lines at 188.23 and 188.30)
Fe XII 195.12
Fe XIII 202.04
Fe XIV 274.20
Fe XV 284.16
Fe XVI 262.99
Fe XVII 254.35
Fe XXIII 263.78
Fe XXIV 192.03
The Fe XXIII and Fe XXIV lines can probably be omitted for
quiet Sun
studies.
One warning for Fe XII: if you pick an exposure time of 30 seconds or
more for an active region, you are likely going to saturate the Fe XII
195 line in parts of the raster simply because EIS is so sensitive at
this wavelength. You thus may want to choose one of the two weaker Fe
XII lines at 192.39 or 193.51 as well as the core 195.12 line in this
case.
Recommended density diagnostics
The following diagnostics involve strong lines and have good
sensitivity to density:
Fe XIII 203.83/202.04
Fe XIII 196.54/202.04
Fe XII 186.88/195.12
The first of these is the best for most conditions. If the
density is
expected to get very high (flares) then it is good to also take the
196.54 line which is sensitive to higher densities. These diagnostics
are discussed in Young et
al. (2009).
Other density diagnostics
Some other useful diagnostics are:
Fe X 257.26/184.54
Si X 258.37/261.04
Fe XI 182.20/188.23
Fe XIV 264.78/274.20
Note that the Fe X 257.26 line lies close to several other
lines. A
large wavelength window is recommended to allow the continuum level to
be assessed properly for this line.
This
page mantained by Dr.P.R.Young,
last revised on 26-Aug-2013
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