A New Look at T Tauri Star Forbidden Lines: MHD-driven Winds from the Inner Disk

Magnetohydrodynamic (MHD) and photoevaporative winds are thought to play an important role in the evolution and dispersal of planet-forming disks. We report the first high-resolution (∆v ∼ 6 km s−1 ) analysis of [S II] λ4068, [O I] λ5577, and [O I] λ6300 lines from a sample of 48 T Tauri stars. Following Simon et al. (2016), we decompose them into three kinematic components: a high-velocity component (HVC) associated with jets, and a low-velocity narrow (LVC-NC) and broad (LVC-BC) components. We confirm previous findings that many LVCs are blueshifted by more than 1.5 km s−1 thus most likely trace a slow disk wind. We further show that the profiles of individual components are similar in the three lines. We find that most LVC-BC and NC line ratios are explained by thermally excited gas with temperatures between 5,000−10,000 K and electron densities ∼ 107 −108 cm−3 . The HVC ratios are better reproduced by shock models with a pre-shock H number density of ∼ 106 − 107 cm−3 . Using these physical properties, we estimate M˙ wind/M˙ acc for the LVC and M˙ jet/M˙ acc for the HVC. In agreement with previous work, the mass carried out in jets is modest compared to the accretion rate. With the likely assumption that the NC wind height is larger than the BC, the LVC-BC M˙ wind/M˙ acc is found to be higher than the LVC-NC. These results suggest that most of the mass loss occurs close to the central star, within a few au, through an MHD driven wind. Depending on the wind height, MHD winds might play a major role in the evolution of the disk mass