Once we have identified a line from some species in our spectral
survey, we may want to search for other lines of that species at
different frequencies. For this, Weeds allows to create a line index,
which works in a similar way as CLASS scan indexes. Scan indexes are
created by the CLASS find
command and they are listed by the
list
command. A given scan from the current index can then be
loaded and plotted using the get
and plot
commands. Likewise, line indexes are created with the lfind
command, listed with the llist
command, and a given line may be
loaded and plotted using the lget
and lplot
commands.
For example, let's assume that we have identified a methanol line on the spectrum shown on Fig. 1, and that we want to see if other methanol lines are present in the spectrum (which covers frequencies between 90 and 100 GHz). The methanol line index is built with:
[fontsize=\scriptsize] LAS90> lfind "CH3OH, vt=0,1" I-SELECT, 36 lines found in the frequency range 89999.6813201 to 100000.269737 MHz
and then listed with:
[fontsize=\scriptsize] LAS90> llist # Species Freq[MHz] Err[MHz] Eup[K] Gup Aij[s-1] Upper level -- Lower level Origin 1 CH3OH, vt=0,1 90295.864 1.754 1234.0 47 1.12e-08 23 +8 15 1 -- 23 +6 17 1 cdms 2 CH3OH, vt=0,1 90812.387 0.232 808.3 41 2.81e-06 20 -3 17 1 -- 19 -2 17 1 cdms 3 CH3OH, vt=0,1 91254.686 0.010 514.3 41 5.31e-08 20 -2 19 0 -- 20 +2 18 0 cdms 4 CH3OH, vt=0,1 92409.579 0.019 44.3 9 5.10e-10 4 +1 3 0 -- 3 -2 2 0 cdms (...) 36 CH3OH, vt=0,1 99776.775 0.649 902.3 41 4.98e-06 20 +3 18 1 -- 21 +4 18 1 cdms
The command prints all methanol lines between 90 and 100 GHz, ordered
by increasing rest frequencies. It also builds an internal index
containing all these lines. Note that the species name must be typed
exactly as it appears in the database and between double quotes, i.e.
"CH3OH, vt=0,1"
in this case.
Like for scans, each line is associated with an entry number, that we
can use to load and to plot the line. Since, by default, lines are
ordered by frequency, subsequent entry numbers will correspond to
lines with increasing frequencies. However, if we search for lines of
a given species, it is usually a good idea to look for lines with the
lowest upper energy levels, because we expect them to be brighter than
higher lying lines. For this, we can re-order the lines by increasing
upper level energies using the /sortby e
option:
[fontsize=\scriptsize] LAS90> lfind "CH3OH, vt=0,1" /sortby e I-SELECT, 36 lines found in the frequency range 89999.6813201 to 100000.269737 MHz LAS90> llist # Species Freq[MHz] Err[MHz] Eup[K] Gup Aij[s-1] Upper level -- Lower level Origin 1 CH3OH, vt=0,1 96741.375 0.005 7.0 5 3.41e-06 2 0 2 +0 -- 1 0 1 +0 cdms 2 CH3OH, vt=0,1 96739.362 0.005 12.5 5 2.56e-06 2 -1 2 0 -- 1 -1 1 0 cdms 3 CH3OH, vt=0,1 96744.550 0.005 20.1 5 3.41e-06 2 +0 2 0 -- 1 +0 1 0 cdms 4 CH3OH, vt=0,1 95914.309 0.005 21.4 5 2.49e-06 2 1 2 +0 -- 1 1 1 +0 cdms (...) 36 CH3OH, vt=0,1 95523.388 1.982 1289.5 49 1.74e-08 24 +8 16 1 -- 24 +6 18 1 cdms
Since we have already identified the first three lines in the index, let's have a look at another one:
[fontsize=\scriptsize] LAS90> lget 4 I-LGET, Found line frequency in the current scan # Species Freq[MHz] Err[MHz] Eup[K] Gup Aij[s-1] Upper level -- Lower level Origin 1 CH3OH, vt=0,1 95914.309 0.005 21.4 5 2.49e-06 2 1 2 +0 -- 1 1 1 +0 cdms
The lget
command modifies the scan frequency so that the
velocity axis is centered at the line rest frequency. We can then use:
[fontsize=\scriptsize] LAS90> lplot
which gives the spectrum shown on Fig. 2.
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The lget
and lplot
commands allow to quickly
``navigate'' in a spectral survey to look for the different lines of a
given species. lget f
will load the first line of the index,
then lget n
will get the next one. lget p
will get the
previous one, etc. If you get lost at some point, you can always type
llist
to display the line index again.