A High-resolution Optical Survey of Upper Sco: Evidence for Coevolution of Accretion and Disk Winds

Abstract

Magnetohydrodynamic (MHD) and photoevaporative winds are thought to play an important role in the evolution and dispersal of planet-forming disks. Here, we analyze high-resolution (Δ v ∼ 7 km s ^−1 ) optical spectra from a sample of 115 T Tauri stars in the ∼5–10 Myr Upper Sco association and focus on the [O i ] λ 6300 and H α lines to trace disk winds and accretion, respectively. Our sample covers a large range of spectral types and we divide it into warm (G0-M3) and cool (later than M3) to facilitate comparison with younger regions. We detect the [O i ] λ 6300 line in 45 out of 87 Upper Sco sources with protoplanetary disks and 32 out of 45 are accreting based on H α profiles and equivalent widths. All [O i ] λ 6300 Upper Sco profiles have low-velocity (centroid < −30 km s ^−1 ; low-velocity component (LVC)) emission and most (36/45) can be fit by a single Gaussian (SC). The single-component (SC) distribution of centroid velocities and FWHMs is consistent with MHD disk winds. We also find that the Upper Sco sample follows the same accretion luminosity−LVC [O i ] λ 6300 relation and the same anticorrelation between SC FWHM and Wide-field Infrared Survey Explorer W3-W4 spectral indices as the younger samples. These results indicate that accretion and disk winds coevolve and that, as inner disks clear out, wind emission arises further away from the star. Finally, our large spectral range coverage reveals that cool stars have larger FWHMs normalized by stellar mass than warm stars indicating that [O i ] λ 6300 emission arises closer in toward lower-mass/lower luminosity stars.

Keywords

• Pre-main sequence stars
• Protoplanetary disks
• Stellar accretion disks
• Magnetohydrodynamics