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We present an analysis of stellar populations in passive galaxies in sevenmassive X-ray clusters at z=0.19-0.89. Based on absorption line strengthsmeasured from our high signal-to-noise spectra, the data support primarilypassive evolution of the galaxies. We use the scaling relations betweenvelocity dispersions and the absorption line strengths to determinerepresentative mean line strengths for the clusters. From the agedeterminations based on the line strengths (and stellar population models), wefind a formation redshift of z_form=1.96(-0.19,+0.24). Based on line strengthmeasurements from high signal-to-noise composite spectra of our data, weestablish the relations between velocity dispersion, ages, metallicities [M/H]and abundance ratios [alpha/Fe] as a function of redshift. The [M/H]-velocitydispersion and [alpha/Fe]-velocity dispersion relations are steep and tight.The age-velocity dispersion relation is flat, with zero point changesreflecting passive evolution. The scatter in all three parameters are within0.08-0.15 dex at fixed velocity dispersions, indicating a large degree ofsynchronization in the evolution of the galaxies. We find indication ofcluster-to-cluster differences in metallicities and abundance ratios. However,variations in stellar populations with the cluster environment can only accountfor a very small fraction of the intrinsic scatter in the scaling relations.Thus, within these very massive clusters the main driver of the properties ofthe stellar populations in passive galaxies appears to be the galaxy velocitydispersion.

Galaxy populations in massive z=0.2-0.9 clusters: I. Analysis of spectroscopy