3.1.17. Ion: select ions for the plasma models¶
3.1.17.1. Overview¶
For the plasma models, it is possible to include or exclude specific groups of ions from the line calculations. This is helpful if a better physical understanding of the (atomic) physics behind the spectrum is requested.
In addition, there is an option to mute particular lines in the spectrum for specific analysis purposes.
There are two main reasons why the user may use this option: computational speed and educational reasons.
3.1.17.1.1. Computational speed¶
The first reason is accelerating the calculations. For complex spectral models, the computational time may be long due to the large number of ions and transitions that need to be taken into account, in particular for the line calculations.
By reducing the number of ions in the calculation, or using a maximum principal quantum number, or other reductions, allow to make the calculations faster by simply skipping the line emission from those transitions. Note that obviously this leads to less accurate spectra as compared to the full calculation. Technically, it is done by using the “ions ignore …” or “ions use …” commands (for getting rid of, or including line emission from specific ions), or the “ions nmax …” or “ions lmax …” commands, to reduce the maximum principal quantum number and the maximum orbital quantum number , respectively. Also, by using the “ions new …”, “ions qc …”, and “ions old …” commands one may switch between the default (new) spex calculations, the quick-cie mode, and the (old) mekal calculations. See Optimizing model performance for more details.
A minor note must be made here: when excluding a single ion, the calculations becomes less accurate, because level populations of ions depend also on how many ionisations or recombinations occur from levels of neighbouring ions. By ignoring an ion, it also cannot contribute to its neighbours.
Currently these settings only affect the line emission; in the calculation of the ionisation balance as well as the continuum always all ions are taken into account (unless of course the abundance is put to zero).
3.1.17.1.2. Diagnostics & education¶
The second reason to include or exclude ions is for diagnostic or educational reasons. It may be of interest to know how the spectrum of a single ion looks, or how the total spectrum would look without an ion. For such cases, SPEX has the “ions mute …” or its inverse “ions unmute …” commands.
Contrary to the use/ignore commands, with this command the full spectrum is calculated, and only at the last step the contribution of the ion is muted or unmuted. Also, contrary to the use/ignore commands, this option works on the full spectrum (continuum and lines, both in emission and absorption). Finally, take care when combining the use/ignore with the mute/unmute commands. Whenever you ignore an ion, it will not be calculated and in those cases the mute or unmute commands are not effective.
Finally, when you use the mute/unmute commands, it will also affect the ascii output for a few important output options, like the “line” and “tra” options for line emission or absorption.
Warning
When using the pion model with this option, you will get a different solution, because it affects the heating and cooling rates, and thus the ionisation balance (equilibrium temperature). Exception is when you use the tmod=1 option for pion, which forces the temperature to be equal to what you prescribe through parameter tinp. For diagnosing the heating/cooling contributions of ions or elements, it is therefore recommended to run first the model with all ions, make an ascii-output of the plasma parameters, take the temperature from there as the “tinp” parameter, and set tmod=1. You can play then with the mute/unmute command.
3.1.17.1.3. Quicklook¶
A new quicklook mode is introduced in SPEX 3.0. This mode can greatly reduce computation time by excluding the atomic levels of outer shells that barely affect the obtained spectrum. The maximum quantum numbers and of Hydrogen-like ions are provided in the table below.
The quicklook mode is enabled by the command:
SPEX> ions ql
To undo the quicklook mode, just type ions use all
.
Warning
This mode will not work for CX model, since electron captured by charge exchange usually populate the outer shells.
Ion |
max. |
max. |
Ion |
max. |
max. |
Ion |
max. |
max. |
---|---|---|---|---|---|---|---|---|
C VI |
16 |
3 |
N VII |
16 |
3 |
O VIII |
16 |
5 |
F IX |
2 |
1 |
Ne X |
16 |
4 |
Na XI |
9 |
2 |
Mg XII |
16 |
4 |
Al XIII |
9 |
2 |
Si XIV |
16 |
4 |
P XV |
5 |
1 |
S XVI |
16 |
4 |
Cl XVII |
4 |
1 |
Ar XVIII |
13 |
2 |
K XIX |
4 |
1 |
Ca XX |
9 |
2 |
Sc XXI |
2 |
1 |
Ti XXII |
4 |
1 |
V XXIII |
2 |
1 |
Cr XXIV |
5 |
1 |
Mn XXV |
4 |
1 |
Fe XXVI |
16 |
4 |
Co XXVII |
2 |
1 |
Ni XXVIII |
8 |
2 |
Cu XXIX |
2 |
1 |
Zn XXX |
2 |
1 |
Note
the quicklook mode is different from the quick CIE mode set by ions qc
or var calc qc
.
3.1.17.1.4. QC mode¶
QC, or the quick cie mode, is introduced in SPEX v3.08 for a quick evalulation of CIE-family models, including CIE, dem, pdem, wdem, cf, and clus. This mode can be turned on and off for individual ions or elements.
Note
ion qc
is only valid when the system flag var calc
is set to new
or qc
.
3.1.17.1.5. Ewlim¶
An alternative, tunable method to reduce the computation time is the ewlim mode. For a grid of temperatures and non-equilibrium ionisation or recombination parameters, for each spectral line in SPEX the maximum equivalent width has been computed. The equivalent width is here the line intensity divided by the continuum intensity for the same model. From this, we compute for each line with E the energy of the line. This is a measure of the relative intensity of the line for a given spectral resolution. Further, for each line we register the maximum principal quantum number .
The user now can select a critical value for (or actually, the 10log of this quantity). Now for each principal quantum number, we check whether there is any line with . If so, all lines with this principal quantum number are retained, but if none of thelines is tronger than the threshold, we will discard lines from that pricipal quantum number. In this way we determine the maximum principal quantum number for each ion, given the value for . Higher values for means less lines, because more lines will be deemed to be too weak.
A performance test shows that a speed gain of a factor of 2-3 gan be reached with this method. It is in particular useful for error searches on parameter values. Try experimenting with this.
Warning
it is advised, after obtaining a best fit with some setting of ewlim, to set the parameter ewlim to -25 (including all lines), issue a calculate command, and compare the cstat value of this model with the cstat value of your fit. Dicide if this is good enough for your purpose.
3.1.17.1.6. Mute lines¶
A new feature since version 3.06.01 is the line mute command. In some cases, when users what to study a particular line, they want to remove the line from the spectrum to replace it, for example, with a delta line or Gaussian.
The ions mute line
command allows to mute up to 10 spectral lines
identified from the asc ter line
output. Please note that this command
only works for SPEXACT v3 (var calc new
). When SPEXACT v3 is enabled, the
ascdump line
command (Ascdump: ascii output of plasma and spectral properties) will show a line list with line
id numbers:
1 O VIII 1s 2S1/2 - 2p 2P1/2 0.6534939 18.97252 1.418E+42 1.689E-06 3.957E-04
2 O VIII 1s 2S1/2 - 2s 2S1/2 0.6535030 18.97225 1.011E+39 1.419E-12 3.957E-04
3 O VIII 1s 2S1/2 - 2p 2P3/2 0.6536802 18.96711 2.834E+42 1.691E-06 3.958E-04
In the example of O VIII above, the line id is listed as an integer in the first column before O VIII. To not show the O VIII Lya lines in the spectrum, they can be muted with the command:
SPEX> ions mute line 1 ion 8 8
SPEX> ions mute line 3 ion 8 8
Where the number behind line
is the line id, and the numbers behind ion
are the atomic number and ionisation stage, respectively. If necessary, the
lines can be unmuted with the ions unmute line
command which has a very
similar syntax.
3.1.17.2. Syntax¶
The following syntax rules apply:
ions show
: Display the list of ions currently taken into accountions ewlim #r
: use only the strongest lines using criterion #r.ions use all
: Use all possible ions in the calculation of the
line spectrum. This is the default at startup of the program.ions use iso #i:
: Use ions of the iso-electronic sequences
indicated by #i: in the line spectrumions use z #i:
: Use ions with the atomic numbers indicated by #i:
in the line spectrumions use ion #i1 #i2:
: Use ions with the atomic number indicated
by #i1 and ionisation stage indicated by #i2: in the line spectrumions ignore all
: Ignore all possible ions in the calculation of the
line spectrumions ignore iso #i:
: Ignore ions of the iso-electronic sequences
indicated by #i: in the line spectrumions ignore z #i:
: Ignore ions with the atomic numbers indicated
by #i: in the line spectrumions ignore ion #i1 #i2:
: Ignore ions with the atomic number
indicated by #i1 and ionisation stage indicated by #i2: in the line
spectrumions unmute all
: Display the contributions of all possible ions
in the final spectrum. This is the default at startup of the program.ions unmute iso #i:
: Display ions of the iso-electronic sequences
indicated by #i: in the spectrumions unmute z #i:
: Display ions with the atomic numbers indicated by #i:
in the spectrumions unmute ion #i1 #i2:
: Display ions with the atomic number indicated
by #i1 and ionisation stage indicated by #i2: in the spectrumions mute all
: Ignore all possible ions in the display of the
spectrum; will create a zero emission or transmission spectrum! Most useful
when followed immieditately by a “ions unmute …” commandions mute iso #i:
: Do not display ions of the iso-electronic sequences
indicated by #i: in the spectrumions ignore z #i:
: Do not display ions with the atomic numbers indicated
by #i: in the spectrumions ignore ion #i1 #i2:
: Do not display ions with the atomic number
indicated by #i1 and ionisation stage indicated by #i2: in the
spectrumions nmax all #i:
: Set maximum for all ionsions nmax iso #i1: #i2
: Set maximum to #i2 for
isoelectronic sequence indicated by #i1ions nmax z #i1: #i2
: Set maximum to #i2 for atomic
number indicated by #i1ions nmax ion #i1 #i2: #i3
: Set maximum to #i3 for
atomic number indicated by #i1 and ionisation stage indicated by #i2.ions lmax all #i:
: Set maximum for all ionsions lmax iso #i1: #i2
: Set maximum to #i2 for
isoelectronic sequence indicated by #i1ions lmax z #i1: #i2
: Set maximum to #i2 for atomic
number indicated by #i1ions lmax ion #i1 #i2: #i3
: Set maximum to #i3 for
atomic number indicated by #i1 and ionisation stage indicated by #i2.ions old all
: Force the old calculation for all ionsions old iso #i1:
: Force the old calculation for the
isoelectronic sequence indicated by #i1ions old z #i1:
: Force the old calculation for atomic number
indicated by #i1ions old ion #i1 #i2:
: Force the old calculation for atomic
number indicated by #i1 and ionisation stage indicated by #i2.ions qc all
: Force the quick-cie calculation for all ionsions qc iso #i1:
: Force the quick-cie calculation for the
isoelectronic sequence indicated by #i1ions qc z #i1:
: Force the quick-cie calculation for atomic number
indicated by #i1ions qc ion #i1 #i2:
: Force the quick-cie calculation for atomic
number indicated by #i1 and ionisation stage indicated by #i2.ions new all
: Force the new calculation for all ionsions new iso #i1:
: Force the new calculation for the
isoelectronic sequence indicated by #i1ions new z #i1:
: Force the new calculation for atomic number
indicated by #i1ions new ion #i1 #i2:
: Force the new calculation for atomic
number indicated by #i1 and ionisation stage indicated by #i2.ions mute line #i1 ion #i2 #i3
: Mute a line with id #i1 for
element #i2 at ionisation stage #i3.ions unmute line #i1 ion #i2 #i3
: Unmute a line with id #i1 for
element #i2 at ionisation stage #i3.3.1.17.3. Examples¶
ions ignore all
: Do not take any line calculation into accountions use iso 3
: Use ions from the (Li) iso-electronic
sequenceions use iso 1:2
: Use ions from the H-like and He-like
isoelectronic sequencesions ignore z 26
: Ignore all iron () ionsions use ion 6 5:6
: Use C V to C VIions mute ion 8 7
: does eliminate the O VII continuum and lines from
the displayed spectrumions unmute iso 2
: shows the emission from all He-like ions (again).ions show
: Display the list of ions that are usedions ql
: Quicklook mode onions ewlim 1.2
: Select strongest lines using the cut-off value 1.2ions old ion 6 6
: Use old calculation for C VIions qc ion 6 5
: Use quick-cie calculation for C Vions nmax ion 26 25 5
: Set maximum principal quantum number for
Fe XXV to .ions lmax ion 26 25 3
: Set maximum angular momentum quantum
number for Fe XXV to .ions mute line 1 ion 8 8
: Mute line id 1 for O VIII.ions unmute line 1 ion 8 8
: Unmute line id 1 for O VIII.