Observing the linked depletion of dust and CO gas at 0.1–10 au in disks of intermediate-mass stars

Abstract

We report on the discovery of correlations between dust and CO gas tracers of the 0.1-10 au region in planet-forming disks around young intermediate-mass stars. The abundance of refractory elements on stellar photospheres decreases as the location of hot CO gas emission recedes to larger disk radii, and as the near-infrared excess emission from hot dust in the inner disk decreases. The linked behavior between these observables demonstrates that the recession of infrared CO emission to larger disk radii traces an inner disk region where dust is being depleted. We also find that Herbig disk cavities have either low (similar to 5-10%) or high (similar to 20-35%) near-infrared excess, a dichotomy that has not been captured by the classic definition of "pre-transitional" disks.