- Form:EWAVE source [XOFF=x0] [PORD=nw] [MORD=nm] [REJ=rej]
[TTY] [TRACE]
-
- source
- is the buffer to be wavelength calibrated.
- XOFF=
- x-offset (column offset) from the nominal
pattern center. It is positive when the CCD
is to the left of the nominal pattern center.
- PORD=
- order of the polynomial to be fit in the x coordinate.
- MORD=
- order of the polynomial to be fit in the 1/m
(1/order number) coordinate.
- REJ=
- hard limit in mA determining the maximum residual
allowed between the wavelength of a line and the
wavelength determined from the fit.
- TTY
- gives a detailed printout of the lines identified and
their residuals.
- TRACE
- traces the fit parameters, printing them out after each
iteration.
EWAVE will first match emission peaks in an extracted echelle arc spectrum
(where the row number of the Vista image corresponds to the order number of
the spectrum in that row, and the column number will be the column from the
original (raw) image). For each order, the program looks for peaks and
attempts to identify them based on an initial estimate of the central
wavelength of that order. It assumes that none of the lines are blended.
After the identifications are made a two-D polynomial is fit using a
non-linear least square method. The two coordinates of this polynomial are
the column number and 1/m where m is the order number. The default orders
of the polynomial are 2 for the column number and 1 for the 1/m coordinate.
It is possible at the moment to fit a 3 x 1 polynomial instead of a 2 x 1
polynomial using PORD=3 but this generally does not improve the accuracy of
the fit. The fit parameters are iterated up to five times.
The `XOFF=' keyword is used when the ccd is offset from the nominal pattern
center (grating rotation = 493830). It is positive when the ccd is to the
left of the pattern center. It is zero by default. The keyword `REJ=' is
invoked to allow the routine to converge more rapidly. A line is rejected
if the difference between the wavelength of the line and its wavelength
determined from the polynomial fit is larger than `rej' mA. It is invoked
after the second iteration and is 100 mA by default.
Examples:
- RD 1 THAR.EXT; EWAVE 1; WD 1 THAR.WAV FULL
- Wavelength
calibrates an echelle image centered on the nominal pattern center
using a two-D polynomial of order 2 for the column number and of
order 1 for 1/m. The input image called "THAR.CCD" was read from
disk and is written back to disk after calibration.
- RD 1 THAR_100.EXT
-
- EWAVE 1 XOFF=100 PORD=2 MORD=1 REJ=75 TTY TRACE
-
- WD 1 THAR_100.WAV FULL
- Wavelength calibrates an echelle
image shifted by 100 pixels to the left from the nominal pattern
center using again a two-D polynomial of order 2 for the column
number and of order 1 for 1/m. All the lines having a residual
larger than 75 mA will be rejected after the second iteration. The
fit parameters, the lines identified and their residuals will be
printed out out after each iteration.