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Fig. 1 shows a part of a spectral
survey3. The
spectrum on the figure shows several well detected lines that we want
to identify. This can be done with lid
which allows us to
select a line on the spectrum with the mouse. Clicking on the left
button of the mouse over some part of the spectrum selects a line.
Then the command searches in the database (which has been selected
previously with the use in
command, as explained above) for
lines within 10 channels of the selected region(s) of the
spectrum4. For each line found, the command marks the
rest frequency of the line on the spectrum, and a table displaying the
line frequency, upper level energy, Einstein coefficient and quantum
numbers and is printed:
[fontsize=\scriptsize] LAS90> lid I-SELECT, 1 lines found in the frequency range 96737.8185473 to 96740.9437312 MHz # Species Freq[MHz] Err[MHz] Eup[K] Gup Aij[s-1] Upper level -- Lower level Origin 1 CH3OH, vt=0,1 96739.362 0.005 12.5 5 2.56e-06 2 -1 2 0 -- 1 -1 1 0 cdms
Most of the time, several line candidates are found for a given
frequency. For example, using lid
to search for lines in the
catalog around the brightest line in Fig. 1,
we obtain:
[fontsize=\scriptsize] LAS90> lid I-SELECT, 4 lines found in the frequency range 96739.7756444 to 96742.9008283 MHz # Species Freq[MHz] Err[MHz] Eup[K] Gup Aij[s-1] Upper level -- Lower level Origin 1 n-C3H7CN 96741.208 0.009 158.0 50 7.60e-06 12 310 1 -- 11 2 9 1 cdms 2 gGG'g-1,3-Propanediol 96741.245 0.030 40.1 31 1.58e-05 15 213 1 -- 14 212 0 cdms 3 C4H, v7=1 96741.314 0.092 214.2 44 3.74e-06 10 111 -- 9-110 cdms 4 CH3OH, vt=0,1 96741.375 0.005 7.0 5 3.41e-06 2 0 2 +0 -- 1 0 1 +0 cdms
Searches in the database may be refined to lines with an upper level
energy lower than a given value using the /energy
option, or to
lines with an Einstein coefficient greater than a given value with the
/aeinstein
option. The /species
option allows to restrict
searches to a given species.
It should be noted that lid
prints the line upper and lower
level quantum numbers exactly as they appear in the selected
database. We refer the user to the documentation of these databases
for the meaning of these quantum numbers.