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We present JHK imaging of 10 moderate-redshift rich galaxy clusters. Near-infrared images of a sample in the range $0.3 \leq z \leq 0.6$ were observed with IRIM II on the 2.1m and SQIID on the 1.3m at Kitt Peak National Observatory. The $\sim$5 arcminute field images reach a depth such that 20\% photometry is obtained on galaxies 1.5 magnitudes fainter than $L_\ast$ at the cluster redshift. As is well known, the near infrared is relatively immune to the effects of evolution and reddening, and samples the peak of the spectral energy distribution in normal galaxies (in $F_\nu$ units). Our data allows us to compare clusters with different redshifts at similar infrared rest wavelengths. In this limited redshift range, we have found that the $J-K$ color is an effective means of distinguishing cluster members from galaxies at other redshifts. The three IR bands allow for better intercomparison among the clusters at different redshifts with less error due to inadequate K-corrections. From this sample, we are building a dataset of JHK photometry of roughly 100 galaxies per cluster. We will combine the new $JHK$ data with the large amount of existing optical photometry in the literature for the lower z clusters, and with the multiband optical photometry obtained by Dickinson for his thesis on the higher z clusters. We will compare optical-to-IR colors and IR color-magnitude diagrams to predictions from isochrone synthesis models (Bruzual and Charlot 1993) with a more complete data set. In particular we will investigate 1) the evidence for a post-burst AGB phase in the optically-red galaxies 2) if the burst activity is caused by mergers or cluster infall; and 3) the strength of the starbursts relative to the overall stellar populations.
