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Session 6 - Evolution, Survey and Clusters of Galaxies.
Display session, Monday, June 10
Tripp Commons,
Hydra multifiber spectroscopic data of the Abell 2255 cluster of galaxies (richness class 2; distance class 3) was collected in June 1992 by Hill et al. and was reduced using the imred.hydra software package in IRAF. The CCD data was flat fielded, sky subtracted, and scattered light subtracted. The observed wavelength coverage was 3500 to 7500 Angtroms with a resolution of 5 Angstroms. The spectra were dispersion corrected with a typical wavelength calibration error of 0.1-0.3 Angstrom RMS. Redshift measurements were performed on the resultant spectra using the cross correlation technique developed by Tonry and Davis. The IRAF rv.fxcor Fourier cross correlation package was used to perform the measurements after logbinning, continuum removal and cosmic ray clipping. The galaxy spectra were correlated against 19 previously collected velocity template spectra from n3379, m31, m32, a779, and a2199. Correlation was also performed against the two a2255 galaxy spectra that provided the highest R-values (> 10). Spurious velocities were removed by clipping those that deviated from the mean by more than 3 standard deviations (a process iterated five times). Redshift measurements of spectra with R > 10 were verified by hand using the Ca K(3933.7A), Ca H(3968.5A), G-band (4304.4), H\beta(4863.9A) and Na D(5892.5A) lines. We obtained 85 redshifts from the Hydra observations. These were combined with an additional 65 redshifts obtained previously with the MX Spectrometer on the Steward 2.3m telescope. Preliminary results from the analysis of the corresponding velocities will be reported.
