RVSAO-2.0 - DIGITAL REDSHIFTS AND RADIAL-VELOCITIES

RVSAO is a set of programs to obtain redshifts and radial velocities f rom digital spectra. RVSAO operates in the IRAF environment. The heart of the system is xcsao, which implements the cross-con-elation method and is a direct descendant of the system built by Tonry & Davis. emsa o uses intelligent heuristics to search for emission lines in spectra, and then fits them to obtain a redshift. sumspec shifts and sums spec tra to build templates for cross-correlation. linespec builds syntheti c spectra given a list of spectral lines. bcvcorr corrects velocities for the motion of the Earth. We discuss in detail the parameters neces sary to run xcsao and emsao properly. We discuss the reliability and e rror associated with xcsao-derived redshifts. We develop an internal e rror estimator, and we show how large, stable surveys can be used to d evelop more accurate error estimators. We also develop a new methodolo gy for building spectral templates for galaxy redshifts, using the new templates for the FAST spectrograph as an example. We show how to obt ain correlation velocities using emission-line templates. Emission-lin e correlations ate substantially more efficient than the previous stan dard technique, automated emission-line fitting. Using this machinery, the blunder rate for redshift measurements can be kept near zero. the automation rate for FAST spectra is similar to 95%. We use emsao to m easure the instrumental zero-point offset and instrumental stability o f the Z-Machine and FAST spectrographs. We compare the use of RVSAO wi th new methods, which use singular value decomposition and chi(2) fitt ing techniques, and conclude that the methods we use are either equal or superior. We show that a two-dimensional spectral classification of galaxy spectra can be developed using our emission- and absorption-li ne templates as physically orthogonal basis vectors.