specshift: Shift spectral dispersion coordinate systems

Package: kpnocoude

Usage

specshift spectra shift

Parameters

spectra: List of spectra to be modified.

shift: Dispersion coordinate shift to be added to the current dispersion coordinate system.

apertures = "": List of apertures to be modified. The null list selects all apertures. A list consists of comma separated numbers and ranges of numbers. A range is specified by a hyphen. An optional step size may be given by using the 'x' followed by a number. See xtools.ranges for more information. This parameter is ignored for N-dimensional spatial spectra such as long slit and Fabry-Perot.

verbose = no: Print a record of each aperture modified?

Description

This task applies a shift to the dispersion coordinate system of selected spectra. The image data is not modified as with imshift but rather the coordinate system is shifted relative to the data. The spectra to be modified are selected by specifying a list of images and apertures. If no aperture list is specified then all apertures in the images are modified. For N-dimensional spatial spectra such as long slit and Fabry-Perot the aperture list is ignored.

The specified shift is added to the existing world coordinates. For linear coordinate systems this has the effect of modifying CRVAL1, for linear "multispec" coordinate systems this modifies the dispersion coordinate of the first physical pixel, and for nonlinear "multispec" coordinate systems this modifies the shift coefficient(s).

It is also possible to shift the linearized coordinate systems (but not the nonlinear coordinate systems) with sapertures or possibly with wcsedit or hedit if the coordinate system is stored with a global linear system.

The verbose parameter lists the images, the apertures, the shift, and the old and new values for the first physical pixel are printed.

Examples

1. To add 1.23 Angstroms to the coordinates of all apertures in the image "ngc456.ms":

cl> specshift ngc456.ms 1.23

Revisions

SPECSHIFT V2.10.3: First version.