RVSAO 2.0: Digital Redshifts and Radial Velocities

RVSAO is a set of programs to obtain redshifts and radial velocities fromdigital spectra. RVSAO operates in the IRAF(Tody 1986, 1993) environment. Theheart of the system is xcsao, which implements the cross-correlation method,and is a direct descendant of the system built by Tonry and Davis (1979). emsaouses intelligent heuristics to search for emission lines in spectra, then fitsthem to obtain a redshift. sumspec shifts and sums spectra to build templatesfor cross-correlation. linespec builds synthetic spectra given a list ofspectral lines. bcvcorr corrects velocities for the motion of the earth. Wediscuss in detail the parameters necessary to run xcsao and emsao properly. We discuss the reliability and error associated with xcsao derived redshifts.We develop an internal error estimator, and we show how large, stable surveyscan be used to develop more accurate error estimators. We develop a new methodology for building spectral templates for galaxyredshifts. We show how to obtain correlation velocities using emission linetemplates. Emission line correlations are substantially more efficient than theprevious standard technique, automated emission line fitting. We compare the use of RVSAO with new methods, which use Singular ValueDecomposition and $\chi^2$ fitting techniques.