Monitoring Inner Regions in the RY Tau Jet

We present multiepoch observations of the RY Tau jet for Hα and [Fe ii] 1.644 μm emission lines obtained with the Subaru Coronagraphic Extreme-AO and Visible Aperture Masking Polarimetric Imager for Resolved Exoplanetary Structures (VAMPIRES), Gemini Near-infrared Integral Field Spectrograph, and Keck/OSIRIS in 2019-2021. These data show a series of four knots within 1″ consistent with the proper motion of ∼0.″3 yr-1, analogous to the jets associated with another few active T Tauri stars. However, the spatial intervals between the knots suggest the time intervals of the ejections of about 1.2, 0.7, and 0.7 yr, significantly shorter than those estimated for the other stars. These Hα images contrast with the archival Very Large Telescope Spectro-Polarimetric High-contrast Exoplanet Research and Zurich IMaging POLarimeter (ZIMPOL) observations from 2015, which showed only a single knot-like feature at ∼0.″25. The difference between the 2015 and 2019-2021 epochs suggests an irregular ejection interval within the six-year range. Such variations of the jet ejection may be related to a short-term (<1 yr) variability of the mass accretion rate. We compared the peaks of the Hα emissions with the ZIMPOL data taken in 2015, showing the brighter profile at the base (<0.″3) than the 2020-2021 VAMPIRES profiles due to time-variable mass ejection rates or the heating-cooling balance in the jet. The observed jet knot structures may be alternatively attributed to stationary shocks, but a higher angular resolution is required to confirm its detailed origin.