Three faint-source microlensing planets detected via resonant-caustic
  channel
  We conducted a project of reinvestigating the 2017--2019 microlensing data
collected by the high-cadence surveys with the aim of finding planets that were
missed due to the deviations of planetary signals from the typical form of
short-term anomalies. The project led us to find three planets including
KMT-2017-BLG-2509Lb, OGLE-2017-BLG-1099Lb, and OGLE-2019-BLG-0299Lb. The
lensing light curves of the events have a common characteristic that the
planetary signals were produced by the crossings of faint source stars over the
resonant caustics formed by giant planets located near the Einstein rings of
host stars. For all planetary events, the lensing solutions are uniquely
determined without any degeneracy. It is estimated that the host masses are in
the range of $0.45\lesssim M/M_\odot \lesssim 0.59$, which corresponds to early
M to late K dwarfs, and thus the host stars are less massive than the sun. On
the other hand, the planets, with masses in the range of $2.1\lesssim M/M_{\rm
J}\lesssim 6.2$, are heavier than the heaviest planet of the solar system, that
is, Jupiter. The planets in all systems lie beyond the snow lines of the hosts,
and thus the discovered planetary systems, together with many other
microlensing planetary systems, support that massive gas-giant planets are
commonplace around low-mass stars. We discuss the role of late-time
high-resolution imaging in clarifying resonant-image lenses with very faint
sources.
