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Stellar-Mass-Dependent Disk Structure in Coeval Planet-Forming Disks

Previous studies suggest that the planet-forming disks around very-low-mass stars/brown dwarfs may be flatter than those around more massive stars, in contrast to model predictions of larger scale heights for gas-disks around lower-mass stars. We conducted a statistically robust study to determine whether there is evidence for stellar-mass-dependent disk structure in planet-forming disks. We find a statistically significant difference in the Spitzer/IRAC color distributions of disks around very-low-mass and low-mass stars all belonging to the same star-forming region, the Chamaeleon I star-forming region. We show that self consistently calculated disk models cannot fit the median spectral energy distributions (SEDs) of the two groups. These SEDs can be only explained by flatter disk models, consistent with the effect of dust settling in disks. We find that relative to the disk structure predicted for flared disks the required reduction in disk scale height is anti-correlated with the stellar mass, i.e. disks around lower-mass stars are flatter. Our results show that the initial and boundary conditions of planet formation are stellar-mass-dependent, an important finding that must be considered in planet formation models.