Population Gradients in Globular Clusters

We report preliminary observations with the WIYN 3.5-m telescope to detect color and composition gradients in globular clusters using the red CN system at 8150 A. Globular clusters in the Milky Way are not simple stellar populations, but rather contain the products of multiple epochs of star formation. In dynamically young clusters, later generations of stars are more centrally concentrated in the clusters and are polluted with elements produced in first generation stars, showing enhanced CN band strengths. These differences suggest that multiple populations can be detected from photometric observations of the red CN system at 8100 A. The new paradigm of multiple stellar populations may provide a context to explain color gradients reported previously in a few globular clusters. The detection of color gradients in the integrated CN color of clusters may also reveal multiple populations in globular clusters in external galaxies