The IRAF/NOAO Spectral World Coordinate Systems

The world coordinate systems for dispersion calibrated spectra used in the IRAF/NOAO spectroscopy packages are presented. In particular, the image header keywords which deene the coordinates. These keywords appear both as part of the IRAF image structure and map directly to FITS format. The types of spectra include multidimensional images with one or more spatial axes and a linear or log-linear dispersion axis and special equispec and multispec formats having multiple independent one dimensional spectra in a single multidimensional image. The multispec format also includes general nonlinear dispersion coordinate systems using polynomial, spline, sampled table, and look-up table functions.