Multi-Epoch NIFS Spectroimaging of the DG Tauri Outflows: New Insights into Protostellar Outflows
The outflows driven by young stellar objects provide important clues to the nature of the underlying accretion-ejection mechanism, as well as probing the physical conditions around the object. In this talk, I present sub-arcsecond-resolution spectroimaging data of the outflows of the young stellar object DG Tauri, obtained using the Near-infrared Integral Field Spectrograph (NIFS) on Gemini North. These data allow us to simultaneously probe the kinematics and structure of the outflows on scales of hundreds of AU. We have rigorously separated the two [Fe II] 1.644 um emission-line components in the approaching outflow for the first time. The high-velocity approaching jet is dominated by moving shock-excited ‘knots’, which emerge with a period of ~5 years and may be linked to observed bursts of accretion activity. The presence of a stationary recollimation shock implies a jet terminal velocity of 400-700 km s-1 and a jet launch radius of 0.02-0.07 AU. We find no sign of jet rotation, which is consistent with a small jet launch radius. Jet acceleration is observed well beyond the height where magnetocentrifugal acceleration should cease. We successfully model this as a form of magnetic acceleration internal to the jet. We model the low-velocity approaching component as a turbulent entrainment layer along the jet boundary, which requires the presence of a ~20-50 mG magnetic field around the jet. The receding outflow takes the form of a large bubble. We propose that this is due to the receding counterjet being blocked by ambient material. Further analysis of our multi-epoch data set will allow us to track the evolution of the outflows over multiple accretion-ejection events.