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FIEStool requires an IRAF patch

FIEStool is a front end to IRAF. The wavelength shift WVLSHIFT calculated by IRAF is given with only 3 digits. For small shifts this translates into 2 decimals which gives an error of up to ~3 m/s because of rounding off before actually shifting the spectrum. When the shift is large WVLSHIFT has only one decimal giving an error of ~30 m/s in the shift and this is certainly too much.

Based on the above it might help to use 4 decimals in WVLSHIFT for high precision work. The below shows how to make IRAF give that precision:

Change the format on line 158 of the file
    /iraf/iraf/noao/onedspec/ecidentify/t_ecreid.x
from
    call fprintf (fd, "%20s %3d/%-3d %3d/%-3d %9.3g %10.3g %7.3g %7.3g\n")
to
    call fprintf (fd, "%20s %3d/%-3d %3d/%-3d %9.3g %12.4f %7.3g %7.3g\n")

Once the change is made you'll need to recompile the package. Login as the 'iraf' user on your system, and check that you have $iraf and $IRAFARCH defined in your unix environment.

Then type the following at the command prompt :

    cd /iraf/iraf/noao
    mkpkg -p noao $IRAFARCH
    cd onedspec
    mkpkg -p noao update

This should make the change.

Back to top Last modified: April 19 2023