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Abstract The Vera C. Rubin Legacy Survey of Space and Time will discover thousands of microlensing events across the Milky Way, allowing for the study of populations of exoplanets, stars, and compact objects. We evaluate numerous survey strategies simulated in the Rubin Operation Simulations to assess the discovery and characterization efficiencies of microlensing events. We have implemented three metrics in the Rubin Metric Analysis Framework: a discovery metric and two characterization metrics, where one estimates how well the light curve is covered and the other quantifies how precisely event parameters can be determined. We also assess the characterizability of microlensing parallax, critical for detection of free-floating black hole lenses. We find that, given Rubin’s baseline cadence, the discovery and characterization efficiency will be higher for longer-duration and larger-parallax events. Microlensing discovery efficiency is dominated by the observing footprint, where more time spent looking at regions of high stellar density, including the Galactic bulge, Galactic plane, and Magellanic Clouds, leads to higher discovery and characterization rates. However, if the observations are stretched over too wide an area, including low-priority areas of the Galactic plane with fewer stars and higher extinction, event characterization suffers by >10%. This could impact exoplanet, binary star, and compact object events alike. We find that some rolling strategies (where Rubin focuses on a fraction of the sky in alternating years) in the Galactic bulge can lead to a 15%–20% decrease in microlensing parallax characterization, so rolling strategies should be chosen carefully to minimize losses. 

Abstract We present an analysis of high-angular-resolution images of the microlensing target MOA-2007-BLG-192 using Keck adaptive optics and the Hubble Space Telescope. The planetary host star is robustly detected as it separates from the background source star in nearly all of the Keck and Hubble data. The amplitude and direction of the lens–source separation allows us to break a degeneracy related to the microlensing parallax and source radius crossing time. Thus, we are able to reduce the number of possible binary-lens solutions by a factor of ∼2, demonstrating the power of high-angular-resolution follow-up imaging for events with sparse light-curve coverage. Following Bennett et al., we apply constraints from the high-resolution imaging on the light-curve modeling to find host star and planet masses ofM_host= 0.28 ± 0.04M_☉and $m_p={12.49}_{-8.03}^{+65.47}{M}_{\oplus }$at a distance from Earth ofD_L= 2.16 ± 0.30 kpc. This work illustrates the necessity for the Nancy Grace Roman Galactic Exoplanet Survey to use its own high-resolution imaging to inform light-curve modeling for microlensing planets that the mission discovers. 

Abstract We report discovering an exoplanet from following up a microlensing event alerted by Gaia. The event Gaia22dkv is toward a disk source rather than the traditional bulge microlensing fields. Our primary analysis yields a Jovian planet with $M_{\mathrm{p}}={0.59}_{-0.05}^{+0.15}{M}_{\mathrm{J}}$at a projected orbital separation $r_{\perp }={1.4}_{-0.3}^{+0.8}$au, and the host is a ∼1.1M_⊙turnoff star at ∼1.3 kpc. At $r\prime \approx 14$, the host is far brighter than any previously discovered microlensing planet host, opening up the opportunity to test the microlensing model with radial velocity (RV) observations. RV data can be used to measure the planet’s orbital period and eccentricity, and they also enable searching for inner planets of the microlensing cold Jupiter, as expected from the “inner–outer correlation” inferred from Kepler and RV discoveries. Furthermore, we show that Gaia astrometric microlensing will not only allow precise measurements of its angular Einstein radiusθ_Ebut also directly measure the microlens parallax vector and unambiguously break a geometric light-curve degeneracy, leading to the definitive characterization of the lens system. 

Aims.We investigated the nature of the anomalies appearing in four microlensing events KMT-2020-BLG-0757, KMT-2022-BLG-0732, KMT-2022-BLG-1787, and KMT-2022-BLG-1852. The light curves of these events commonly exhibit initial bumps followed by subsequent troughs that extend across a substantial portion of the light curves. Methods.We performed thorough modeling of the anomalies to elucidate their characteristics. Despite their prolonged durations, which differ from the usual brief anomalies observed in typical planetary events, our analysis revealed that each anomaly in these events originated from a planetary companion located within the Einstein ring of the primary star. It was found that the initial bump arouse when the source star crossed one of the planetary caustics, while the subsequent trough feature occurred as the source traversed the region of minor image perturbations lying between the pair of planetary caustics. Results.The estimated masses of the host and planet, their mass ratios, and the distance to the discovered planetary systems are (M_host/M_⊙,M_planet/M_J,q/10⁻³,D_L/kpc) = (0.58_−0.30^+0.33, 10.71_−5.61^+6.17, 17.61 ± 2.25, 6.67_−1.30^+0.93) for KMT-2020-BLG-0757, (0.53_−0.31^+0.31, 1.12_−0.65^+0.65, 2.01 ± 0.07, 6.66_−1.84^+1.19) for KMT-2022-BLG-0732, (0.42_−0.23^+0.32, 6.64_−3.64^+4.98, 15.07 ± 0.86, 7.55_−1.30^+0.89) for KMT-2022-BLG-1787, and (0.32_−0.19^+0.34, 4.98_−2.94^+5.42, 8.74 ± 0.49, 6.27_−1.15^+0.90) for KMT-2022-BLG-1852. These parameters indicate that all the planets are giants with masses exceeding the mass of Jupiter in our solar system and the hosts are low-mass stars with masses substantially less massive than the Sun. 

Abstract We analyze the MOA-2020-BLG-208 gravitational microlensing event and present the discovery and characterization of a new planet, MOA-2020-BLG-208Lb, with an estimated sub-Saturn mass. With a mass ratio q = 3.17 − 0.26 + 0.28 × 10 − 4 , the planet lies near the peak of the mass-ratio function derived by the MOA collaboration and near the edge of expected sample sensitivity. For these estimates we provide results using two mass-law priors: one assuming that all stars have an equal planet-hosting probability, and the other assuming that planets are more likely to orbit around more massive stars. In the first scenario, we estimate that the lens system is likely to be a planet of mass m planet = 46 − 24 + 42 M ⊕ and a host star of mass M host = 0.43 − 0.23 + 0.39 M ⊙ , located at a distance D L = 7.49 − 1.13 + 0.99 kpc . For the second scenario, we estimate m planet = 69 − 34 + 37 M ⊕ , M host = 0.66 − 0.32 + 0.35 M ⊙ , and D L = 7.81 − 0.93 + 0.93 kpc . The planet has a projected separation as a fraction of the Einstein ring radius s = 1.3807 − 0.0018 + 0.0018 . As a cool sub-Saturn-mass planet, this planet adds to a growing collection of evidence for revised planetary formation models. 

ABSTRACT We report the discovery and analysis of a planet in the microlensing event OGLE-2018-BLG-0799. The planetary signal was observed by several ground-based telescopes, and the planet-host mass ratio is q = (2.65 ± 0.16) × 10−3. The ground-based observations yield a constraint on the angular Einstein radius θE, and the microlensing parallax vector $$\boldsymbol{{\pi} }_{\rm E}$$, is strongly constrained by the Spitzer data. However, the 2019 Spitzer baseline data reveal systematics in the Spitzer photometry, so there is ambiguity in the magnitude of the parallax. In our preferred interpretation, a full Bayesian analysis using a Galactic model indicates that the planetary system is composed of an $$M_{\rm planet} = 0.26_{-0.11}^{+0.22}M_{\rm J}$$ planet orbiting an $$M_{\rm host} = 0.093_{-0.038}^{+0.082}~\mathrm{M}_{\odot }$$, at a distance of $$D_{\rm L} = 3.71_{-1.70}^{+3.24}$$ kpc. An alternate interpretation of the data shifts the localization of the minima along the arc-shaped microlens parallax constraints. This, in turn, yields a more massive host with median mass of $$0.13 {\, \mathrm{M}_{\odot }}$$ at a distance of 6.3 kpc. This analysis demonstrates the robustness of the osculating circles formalism, but shows that further investigation is needed to assess how systematics affect the specific localization of the microlens parallax vector and, consequently, the inferred physical parameters.