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Item Systematic Reanalysis of KMTNet Microlensing Events. II. Two New Planets in Giant-source Events(IOP Publishing on behalf of the American Astronomical Society., 2025-06-01) Yang H; Yee JC; Zhang J; Lee C-U; Kim D-J; Bond IA; Udalski A; Hwang K-H; Zang W; Qian Q; Gould A; Mao S; Albrow MD; Chung S-J; Han C; Jung YK; Ryu Y-H; Shin I-G; Shvartzvald Y; Cha S-M; Kim H-W; Kim S-L; Lee D-J; Lee Y; Park B-G; Pogge RW; Abe F; Bando K; Bennett DP; Bhattacharya A; Fukui A; Hamada R; Hamada S; Hamasaki N; Hirao Y; Silva SI; Itow Y; Koshimoto N; Matsubara Y; Miyazaki S; Muraki Y; Nagai T; Nunota K; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Terry SK; Tristram PJ; Vandorou A; Yama H; Mróz P; Skowron J; Poleski R; Szymański MK; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona MIn this work, we continue to apply the updated KMTNet tender-love care photometric pipeline to historical microlensing events. We apply the pipeline to a subsample of events from the KMTNet database, which we refer to as the giant source sample. Leveraging the improved photometric data, we conduct a systematic search for anomalies within this sample. The search successfully uncovers four new planet-like anomalies and recovers two previously known planetary signals. After detailed analysis, two of the newly discovered anomalies are confirmed as clear planets: KMT-2019-BLG-0578 and KMT-2021-BLG-0736. Their planet-to-host mass ratios are q ∼ 4 × 10−3 and q ∼ 1 × 10−4, respectively. Another event, OGLE-2018-BLG-0421 (KMT-2018-BLG-0831), remains ambiguous. Both a stellar companion and a giant planet in the lens system could potentially explain the observed anomaly. The anomaly signal of the last event, MOA-2022-BLG-038 (KMT-2022-BLG-2342), is attributed to an extra source star. Within this sample, our procedure doubles the number of confirmed planets, demonstrating a significant enhancement in the survey sensitivity.Item Adaptive Optics Imaging Can Break the Central Caustic Cusp Approach Degeneracy in High-magnification Microlensing Events(IOP Publishing on behalf of the American Astronomical Society, 2022-11-01) Terry SK; Bennett DP; Bhattacharya A; Koshimoto N; Beaulieu J-P; Blackman JW; Bond IA; Cole AA; Lu JR; Marquette JB; Ranc C; Rektsini N; Vandorou AWe report new results for the gravitational microlensing target OGLE-2011-BLG-0950 from adaptive optics images using the Keck Observatory. The original analysis by Choi et al. and reanalysis by Suzuki et al. report degenerate solutions between planetary and stellar binary lens systems. This particular case is the most important type of degeneracy for exoplanet demographics because the distinction between a planetary mass or stellar binary companion has direct consequences for microlensing exoplanet statistics. The 8 and 10 yr baselines allow us to directly measure a relative proper motion of 4.20 ± 0.21 mas yr−1, confirming the detection of the lens star system and ruling out the planetary companion models that predict a ∼4× smaller relative proper motion. The Keck data also rule out the wide stellar binary solution unless one of the components is a stellar remnant. The combination of the lens brightness and close stellar binary light-curve parameters yields primary and secondary star masses of M A = 1.12 − 0.09 + 0.11 and M B = 0.47 − 0.10 + 0.13 M ☉ at a distance of D L = 6.70 − 0.30 + 0.55 kpc and a projected separation of 0.39 − 0.04 + 0.05 au. Assuming that the predicted proper motions are measurably different, the high-resolution imaging method described here can be used to disentangle this degeneracy for events observed by the Roman exoplanet microlensing survey using Roman images taken near the beginning or end of the survey.Item OGLE-2014-BLG-0319: A Sub-Jupiter-mass Planetary Event Encountered Degeneracy with Different Mass Ratios and Lens-source Relative Proper Motions(IOP Publishing on behalf of the American Astronomical Society, 2022-03-01) Miyazaki S; Suzuki D; Udalski A; Koshimoto N; Bennett DP; Sumi T; Rattenbury N; Cheongho H; Abe F; Barry RK; Bhattacharya A; Bond IA; Fukui A; Fujii H; Hirao Y; Silva SI; Itow Y; Kirikawa R; Kondo I; Munford B; Matsubara Y; Matsumoto S; Muraki Y; Okamura A; Olmschenk G; Ranc C; Satoh YK; Toda T; Tristram PJ; Yama H; Yonehara A; Poleski R; Mróz P; Skowron J; Szymański MK; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Wyrzykowski ŁWe report the discovery of a sub-Jovian-mass planet, OGLE-2014-BLG-0319Lb. The characteristics of this planet will be added into a future extended statistical analysis of the Microlensing Observations in Astrophysics (MOA) collaboration. The planetary anomaly of the light curve is characterized by MOA and OGLE survey observations and results in three degenerate models with different planetary-mass ratios of q = (10.3, 6.6, 4.5) × 10-4. We find that the last two models require unreasonably small lens-source relative proper motions of μ rel ∼1 mas yr-1. Considering Galactic prior probabilities, we rule out these two models from the final result. We conduct a Bayesian analysis to estimate physical properties of the lens system using a Galactic model and find that the lens system is composed of a 0.49-0.27+0.35MJup sub-Jovian planet orbiting a 0.47-0.25+0.33M⊙ M dwarf near the Galactic Bulge. This analysis demonstrates that Galactic priors are useful to resolve this type of model degeneracy. This is important for estimating the mass-ratio function statistically. However, this method would be unlikely successful in shorter timescale events, which are mostly due to low-mass objects, like brown dwarfs or free-floating planets. Therefore, careful treatment is needed for estimating the mass-ratio function of the companions around such low-mass hosts, which only the microlensing can probe.Item An Isolated Stellar-mass Black Hole Detected through Astrometric Microlensing(IOP Publishing on behalf of the American Astronomical Society, 2022-07-06) Sahu KC; Anderson J; Casertano S; Bond HE; Udalski A; Dominik M; Calamida A; Bellini A; Brown TM; Rejkuba M; Bajaj V; Kains N; Ferguson HC; Fryer CL; Yock P; Mróz P; Kozłowski S; Pietrukowicz P; Poleski R; Skowron J; Soszyński I; Szymański MK; Ulaczyk K; Wyrzykowski Ł; Barry RK; Bennett DP; Bond IA; Hirao Y; Silva SI; Kondo I; Koshimoto N; Ranc C; Rattenbury NJ; Sumi T; Suzuki D; Tristram PJ; Vandorou A; Beaulieu J-P; Marquette J-B; Cole A; Fouqué P; Hill K; Dieters S; Coutures C; Dominis-Prester D; Bennett C; Bachelet E; Menzies J; Albrow M; Pollard K; Gould A; Yee JC; Allen W; Almeida LA; Christie G; Drummond J; Gal-Yam A; Gorbikov E; Jablonski F; Lee C-U; Maoz D; Manulis I; McCormick J; Natusch T; Pogge RW; Shvartzvald Y; Jørgensen UG; Alsubai KA; Andersen MI; Bozza V; Novati SC; Burgdorf M; Hinse TC; Hundertmark M; Husser T-O; Kerins E; Longa-Peña P; Mancini L; Penny M; Rahvar S; Ricci D; Sajadian S; Skottfelt J; Snodgrass C; Southworth J; Tregloan-Reed J; Wambsganss J; Wertz O; Tsapras Y; Street RA; Bramich DM; Horne K; Steele IAWe report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star of the long-duration (t E ≃ 270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462 (hereafter designated as MOA-11-191/OGLE-11-462), in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of 6 yr, reveals a clear relativistic astrometric deflection of the background star's apparent position. Ground-based photometry of MOA-11-191/OGLE-11-462 shows a parallactic signature of the effect of Earth's motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 ± 1.3 M ⊙ and a distance of 1.58 ± 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic disk stars at similar distances by an amount corresponding to a transverse space velocity of �1/445 km s-1, suggesting that the BH received a "natal kick"from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial velocity measurements of Galactic X-ray binaries and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first for an isolated stellar-mass BH using any technique.