Arcturus and the origin of the coronal graveyard

Red giants like Arcturus occupy a region in the Xray HertzsprungRussellDiagram (HRD) known as the coronal graveyard. The physical cause for the sharpdecline of Xray emission beyond a socalled dividing line that separates Xrayemitting yellow giants from Xray dark red giants is, despite decades ofresearch, not finally answered. The recent Xray detection of Arcturus withChandra HRCI motivates our request to obtain spectral information withXMMNewton EPIC spectroscopy. An 80 ks exposure is sufficient to detect largeabsorbing column densities that may be expected if severe obscuration by layersabove the giant.s corona cause the decrease in their observed Xray luminosity. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]