Monitoring inner regions in the RY Tau jet
  We present multi-epoch observations of the RY~Tau jet for H$\alpha$ and
[\ion{Fe}{2}] 1.644 \micron~emission lines obtained with
Subaru/SCExAO+VAMPIRES, Gemini/NIFS, and Keck/OSIRIS in 2019--2021. These data
show a series of four knots within 1$\arcsec$ consistent with the proper motion
of $\sim$0\farcs3~yr$^{-1}$, analogous to the jets associated with another few
active T-Tauri stars. However, the spatial intervals between the knots suggest
the time intervals of the ejections of about 1.2, 0.7, and 0.7 years,
significantly shorter than those estimated for the other stars. These H$\alpha$
images contrast with the archival VLT/SPHERE/ZIMPOL observations from 2015,
which showed only a single knot-like feature at $\sim0\farcs25$. 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 ($<$1 year) variability of the mass accretion rate. We compared
the peaks of the H$\alpha$ emissions with the ZIMPOL data taken in 2015,
showing the brighter profile at the base ($<0\farcs3$) 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.
