ydistcor

ydistcor.cl

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

  1. 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
Last modified: 07/13/2017 02:41
Send questions or comments to:NIRSPEC Support

The information on this page is the property of the W. M. Keck Observatory. The contents of this page or any part thereof shall not be copied or otherwise reproduced or transferred to other documents or used or disclosed to others for any purpose other than observing support at the W. M. Keck Observatory and the subsequent analysis and publication of scientific data obtained from observations conducted at the W. M. Keck Observatory. All rights reserved. © W. M. Keck Observatory.