Time-variable Jet Ejections from RW Aur A, RY Tau, and DG Tau

We present Gemini-NIFS, Very Large Telescope-SINFONI, and Keck-OSIRIS observations of near-IR [Fe ii] emission that are associated with well-studied jets from three active T Tauri stars—RW Aur A, RY Tau, and DG Tau—taken from 2012 to 2021. We primarily cover the redshifted jet from RW Aur A and the blueshifted jets from RY Tau and DG Tau, in order to investigate long-term time variabilities that are potentially related to the activities of mass accretion and/or the stellar magnetic fields. All of these jets consist of several moving knots, with tangential velocities of 70-240 km s⁻¹, which were ejected from the star with different velocities and at irregular time intervals. Via comparisons with the literature, we identify significant differences in the tangential velocities between 1985-2008 and 2008-2021 for the DG Tau jet. The sizes of the individual knots appear to increase with time, and, in turn, their peak brightnesses in the 1.644 μm emission decreased by up to a factor of ∼30 during the epochs of our observations. The variety of decay timescales measured in the [Fe ii] 1.644 μm emission could be attributed to different preshock conditions should the moving knots be unresolved shocks. However, our data do not exclude the possibility that these knots are due to nonuniform density/temperature distributions with another heating mechanism, or, in some cases, due to stationary shocks without proper motions. Spatially resolved observations of these knots with significantly higher angular resolutions will be necessary to better understand their physical nature.