velset: Set velocity by modifying starting wavelength
Package: rvsao
Usage
velset input output
Description
This task changes the wavelength scale of spectra, moving them from one given redshift to another one. The input spectra are specified by an image template list. The output is either a matching list of spectra or a directory. The task works by copying the input spectra to the output destination, and then modifying the header keywords that describe the wavelength axis, on the output spectra only. A spectrum may not be copied onto itself; this prevents original wavelength information from being accidently overwritten. Image sections are ignored both on input and output, because it is assumed that the user wants a copy of the input with the wavelength scale modified.
*** WARNING *** Use this task on log-wavelength spectra ONLY. SUMSPEC will rebin and shift linear wavelength spectra.
This task looks in the header for keywords describing the wavelength axis; keywords are sought in the following order: first, IRAF keywords 'W0' and 'WPC'; next, CD keywords 'CRVALn' and 'CDn_1'; and finally, FITS keywords 'CRVALn' and 'CDELTn' (n is the value of task parameter 'axis', unless the IRAF header keyword 'DISPAXIS' is found, in which case it takes precedence over the parameter). Logarithmic wavelength scale is treated correctly if either the 'log' task parameter is set to "yes" or if the IRAF header keyword 'DC-FLAG' is found in the header with value 1. 'HISTORY' records are appended to the header.
Parameters
- input [file name template]
- Name(s) of the input files containing spectra.
- output [file name or directory name]
- The output file, or directory, to which the transformed spectra will be written.
- velz=yes
- Is the new redshift in Z (yes) or km/sec (no)
- newz = 0.0
- The redshift of the output spectra.
- (verbose = yes) [boolean]
- Print operations? If set to "yes", the wavelength origin and step for both the input and output spectra are listed as the task progresses.
Examples
1. Transform a set of spectra with root name 'cluster*' to redshift 0.0. The result will be stored in subdirectory 'local/'. The input spectra are in STSDAS format (extension '.hhh').
to> setvel cluster*.hhh local/ newz=0.0