Gap Opening and Inner Disk Structure in the Strongly Accreting Transition Disk of DM Tau

Abstract

Large inner dust gaps in transition disks are frequently posited as evidence of giant planets sculpting gas and dust in the disk, or the opening of a gap by photoevaporative winds. Although the former hypothesis is strongly supported by the observations of planets and deep depletions in gas within the gap in some disks, many T Tauri stars hosting transition disks accrete at rates typical for an undepleted disk, raising the question of how gap opening occurs in these objects. We thus present an analysis of the structure of the transition disk around the T Tauri star DM Tau, which is strongly accreting (∼10−8.3 M ⊙ yr−1) and turbulent (α = 0.078 ± 0.02). Using the Dust And LInes thermochemical code, we fit disk models to simultaneously reproduce the accretion rate, high level of turbulence, the gas traced by ALMA Band 6 observations of 12CO, 13CO, and C18O J = 2–1 lines, and the observed dust emission from the millimeter continuum and spectral energy distribution. We find a shallow depletion in gas surface density of ∼10 relative to the outer disk and a gas-rich inner disk that is consistent with the observations. The planet mass of <1 M Jup implied by the gap depth is in tension with predictions for dust trapping in a highly viscous disk, which requires a more massive planet of ∼10 M Jup. Photoevaporative models including a dead zone can qualitatively reproduce some features of the DM Tau disk, but still struggle to explain the high accretion rates and the observed millimeter-continuum flux.