Name
ydistcor -- align emission features with image rows
Usage
ydistcor input output ref
Parameters
- input
- Names of input 2-D spectra to be corrected
- output
- Names of output 2-D spectra to be created
- ref
- Name of reference image
- x1
- First column to extract
- x2
- Last column to extract
- dy=0
- Change in row (y) value for features as they move from
column x1 to column x2. Note that if the features move toward
lower row numbers (as generally done with NIRSPEC images), the
value for dy should be negative.
Description
Given an input image input plus a range of columns
x1-x2, this task shifts the columns as needed to align
emission features with the image rows and thus make reasonable sky
subtraction possible during the spectral extraction phase of data
reduction.
For the selected range of columns, the
longslit.identify task is used non-interactively to
find any bright emission features in the image. Next,
the reidentify task is used to find these same features
in other columns, co-adding data as needed in order to have not
more than a certain number of independent fits for a given
aperture. The fitcoords task is used to find a
solution which fits the coordinates with a polynomial which is
third order in x and second order in y. Then the
transform task will straighten the image.
Examples
- A set of NIRSPEC images taken with the same instrument
settings is to be corrected for y distortion.
Inspection of the first image (24des0022.fits)
shows that the illuminated region extends from column 600 to
column 800. Inspection also reveals that a prominent emission
line the middle of the image begins at row 550 on the left of
the slit and ends at row 525 on the right of the slit.
The task is run with the following parameters:
ydistcor *.fits *%.fits%y.fits% 24des0022 x1=600 x2=800 dy=-25
The new images will be given the same name as the
corresponding input images, with a y appended to
the rootname.
Notes
- The x distortion must already have been removed from the
input image.
Bugs
See Also
identify
reidentify
fitcoords
transform
The cl script ydistcor.cl
The package wmkonspec