Variability and Jet Activity in the YSO MHO 3252 Y3 in Serpens South

The infrared young stellar outflow source MHO 3252 Y3 in the Serpens South star-forming region was found to be variable. The available photometric data can be fitted with a double-peaked light curve with a period of 904 days. Color variations are consistent with variable extinction with a flatter wavelength dependence than interstellar extinction, i.e., larger grains. MHO 3252 Y3 is the source of a large-scale bipolar outflow, but the most recent outflow activity has produced a microjet detectable in the shock-excited H(2 )1-0 S(1) line, while [Fe II] emission appears confined to the immediate vicinity of the central star. The proper motion of individual shock fronts in the H-2 microjet has been measured and traces these knots back to ejection events in the past two centuries. Integral field spectroscopy with the Keck 1 adaptive optics system and the OSIRIS instrument shows velocity components near the launch region that are distinct from the microjet in both radial velocity and apparent proper motion. They match the prediction of dual wind models with a distinct low-velocity disk wind component. We find evidence for the entrainment of this low-velocity component into the high-velocity microjet, leading to shock-excited emission at intermediate velocities in an envelope around the microjet.