Two Low-Mass-Ratio Microlensing Planets from High-Magnification Events: KMT-2021-BLG-0247 and MOA-2023-BLG-169

We present an analysis of two planetary microlensing events, KMT-2021-BLG-0247 and MOA-2023-BLG-169, both of which exhibit high magnifications and low planet--host mass ratios, but with markedly different levels of parameter constraint. For KMT-2021-BLG-0247, the finite-source effect and microlens parallax are both clearly detected, leading to unusually tight constraints on the physical properties of the lens system. The host mass and lens distance are approximately M L=0.9 plus or minus0.1,M and D L=6.7+1.0-0.3, kpc, respectively, and the planet mass is M p=41 plus or minus5,M. The projected planet--host separations are a=3.4+0.7-0.3, au and 3.0+0.6-0.3, au for the wide and close solutions, respectively. In contrast, MOA-2023-BLG-169 involves an extremely faint source, with I S, OGLE=26.73, such that the light curve permits a broad family of strongly correlated solutions. We therefore construct the physical-parameter likelihood using approximate invariant combinations of the light-curve parameters and supplement it with post-event Euclid/VIS imaging from the Euclid Q2 Galactic Bulge Survey (Beaulieu et al. 2026). The Euclid data reveal a component at the event position with VIS AB=23.05 plus or minus0.09, mag. Interpreting this component as the combined light from the source and any luminous lens, the resulting posterior gives M L=0.48+0.23-0.17,M, D L=3.50+2.82-1.20, kpc, a=1.62+0.77-0.43, au, and M p=143+103-63,M. MOA-2023-BLG-169 demonstrates that, for an extreme faint-source event, even the event timescale and angular Einstein radius can remain strongly dependent on the Galactic prior and independent flux constraints.