eqwidth is an
IRAF task in the
rvsao package which
computes equivalent widths for absorprtion or emission lines.
It is based on the IRAF task noao.onedspec.sbands, but allows you to
compute equivalent widths for any band of a multispec spectrum and
redshifts the given rest wavelength regions based on the value of the
VELOCITY or APVEL header keyword.
We have found that automatic cosmic ray rejection in extraction
of a spectrum from a 2-D image can change the equivalent width
of some lines. We recommend using uncleaned spectra for equivalent
widths in such situations. That would be the second spectrum in
IRAF multispec files which have been cleaned, the third being the
background which was removed, and the fourth being the raw extracted