086091

Clusters of galaxies in optical imaging surveys like the DES have the statistical power to be the single most constraining probe of dark energy. However comma realizing this potential relies on our ability to control for systematics comma the largest remaining of which are the effects of projection on cluster selection and mass determinations. We propose XMM observations of six DES clusters where existing spectroscopy indicates a significant contamination from projection-correlated structure resulting in high velocity dispersions for their richness. These data comma along with existing data for an additional five clusters comma will allow us to understand the origin of this population openPartruly massive clusters comma low mass clusters comma unvirialized projectionsclosePar and their contribution to the DES cluster catalog.