- Form: LINEID source [FILE=xxx] [ADD] [TTY] [INT] [CEN=]
[DISP=]
-
- [LAMBDA=wave,pix[,uncer]] [redirection]
- source
- selects the spectrum used in the calibration,
- FILE=
- is a file of line identifications,
- ADD
- will add newly identified lines to a list
of lines from a previous execution of LINEID,
- TTY
- sends more extensive output to the terminal,
- INT
- allows interactive selection of lines,
- CEN=
- allows the user to guess a central wavelength,
- DISP=
- allows the user to guess a dispersion.
- LAMBDA=
- allow the user to preset a (lambda,pixel) pair
LINEID will match emission-lines in a wavelength calibration spectrum with
tables of known line wavelengths. The routine looks for peaks and attempts
to identify them based on an initial estimate of the reciprocal dispersion
in Angstroms/pixel and a list of line identifications read from a file in
in the spectrum directory (SEE PRINT DIRECTORIES) with name 'xxx.WAV'.
Accurate line centers are calculated, and if specified in the data file,
partial line blends deconvolved. The matched lines are saved into a common
block in VISTA. The contents of the common block can be examined using the
command 'PRINT LINEID'. By default, the previous contents of the common
block are replaced with the current identifications. However, if you use
the 'ADD' keyword the new identifications will be appended to the older
results. This allows you to combine the identifications from several
independent wavelength calibration spectra. If the keyword 'INT' is
specified, interactive line identifications can be made. Once your line
list has been created with LINEID you use the WSCALE command to fit a
polynomial to the wavelengths as a function of pixel number.
Normally the first guess as to the dispersion of the wavelength fit (and
the second order term in the fit) are given as the first line of the
wavelength list. (The central wavelength is then left as a free
parameter.) However, the starting dispersion guess may be specified via
the DISP= keyword (specifying two numbers here allows the second order term
to be input as well). Also, using the CEN= keyword allows the user to
input a starting guess for the central wavelength, a necessary feature in
high-resolution work where the line lists are prohibitively long.
In instances where you have a small number of lines in your calibration
spectrum the automatic line identification algorithm may find several
possible matches between the observed lines and the wavelengths given in
your line list. In these instances the LAMBDA= option may help to identify
the correct match. You need to know the approximate wavelength of one
point in your spectrum. With the LAMBDA= keyword you specify a wavelength,
a pixel number for that wavelength, and an uncertainty in that pixel
number. The line identification algorithm will then reject any set of
line/wavelength identifications which are inconsistent with the given
pixel/wavelength pair. For this option to work you much choose a pixel
which lies between identified lines in your spectrum; don't use a pixel
near the ends of your spectrum.
If you only specify the wavelength and pixel number with the LAMBDA= option
then the pixel uncertainty will default to 1. You may want to supply a
larger value though to avoid rejecting all line identifications.
In these examples, assume the default spectrum directory is
ccd/spec:
- LINEID 4 FILE=NEON
- Matches lines in spectrum 4 with the
wavelengths supplied in ccd/spec/NEON.WAV. The resulting
identifications replace any previously saved identifications in the
common block.
- LINEID 4 FILE=NEON >id.txt
- Does the same as example 1, but
this time sending the output to the file id.txt in the current
working directory.
- LINEID 4 INT FILE=NEON ; LINEID 5 TTY FILE=MERCURY ADD
- The
first command does the same as example 1, but allows the user to
make additional line identifications after the command has made its
best attempt. The second command works on a separate mercury lamp
spectrum in buffer 5. The identifications are added to those for
the neon spectrum.
- LINEID 10 FILE=THAR CEN=6715.4 DISP=0.134
- Attempts a
wavelength calibration using the line list THAR.WAV and starting
guesses for the central wavelength of 6715.4 Angstroms and for the
dispersion of 0.134 Angstroms.
The wavelength file has the following format: The file is formatted, with
the first line showing the estimated dispersion, followed by any
second-order term. The format is free, but the second-order term must be
0.0 if it is to be ignored. Subsequent lines contain an ordered set of
line wavelengths in Angstroms. One spectral line is given per file
line. The wavelength if followed by a two-letter ID code. If the code is
CO, that line is ignored. The code is followed by the wavelengths of any
blue-side or red-side satellites which might be blended with the primary
line. The wavelengths must be set to 0.0 if there are no lines blended
with the primary.
Example file:
7.86 |
1.0E-03 |
|
|
5881.4900 |
NE |
5852.4900 |
0.0 |
5944.8300 |
NE |
0.0 |
5975.2800 |
6030.0000 |
NE |
0.0 |
0.0 |
6096.1600 |
NE |
6074.3400 |
6143.0600 |