EMSAO: Radial Velocities from Emission Lines in Spectra

Many extragalactic objects for which radial velocities are desired display strong emission lines. For large surveys, the interactive determination of line centers and calculation of redshifts is too slow. The EMSAO task of the RVSAO IRAF package automatically finds emission lines, fits them with single or multiple Gaussians, and combines the determined redshifts weighting them by the uncertainty in the line centers. In addition to being used in the CfA and other redshift surveys, EMSAO has been used to study sky line shifts in 15 years of observations to characterize the uncertainty in instrumental measurements.