# # Program information file # PROGRAM_ID 2021A014 PROGRAM_TITLE Surface Accretion Flows in Protoplanetary Disks PROGRAM_INV1 John Carr PROGRAM_INV2 Joan Najita PROGRAM_INV3 Sean Brittain PROGRAM_INV4 PROGRAM_INV5 PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG Although disk accretion is fundamental to the formation of stars and planets, the physical mechanism that drives it remains uncertain and a long-standing challenge. Recent observations of the Class I source GV Tau N reveal kinematic evidence for inflow in its disk atmosphere, at a rate comparable to T Tauri stellar accretion rates, providing support for the theoretical idea of disk accretion via surface accretion flows. Our goal is to further explore this idea by identifying and studying additional examples of surface accretion flows. We propose to use iSHELL to measure high-resolution absorption spectra of molecules [HCN, C2H2, H2O and CO] toward GSS 30, a Class I object whose CO fundamental lines show red-shifted absorption profiles similar to those of GV Tau. These measurements will provide velocity profiles, molecular column densities, and gas temperatures, which in turn will allow us to determine whether the redshifted molecular gas arises in the inflowing atmosphere of the inner disk. Our study will potentially provide additional observational support for surface accretion flows as a disk accretion mechanism in protoplanetary disks. PROGRAM_ABSTRACT_END