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Aims. Light curves of microlensing events occasionally deviate from the smooth and symmetric form of a single-lens single-source event. While most of these anomalous events can be accounted for by employing a binary-lens single-source (2L 1S) or a single-lens binary-source (1L2S) framework, it is established that a small fraction of events remain unexplained by either of these interpretations. We carried out a project in which data collected by high-cadence microlensing surveys were reinvestigated with the aim of uncovering the nature of anomalous lensing events with no proposed 2L 1S or 1L 2S models. Methods. From the project we found that the anomaly appearing in the lensing event OGLE-2023-BLG-0836 cannot be explained by the usual interpretations, and we conducted a comprehensive analysis of the event. From thorough modeling of the light curve under sophisticated lens-system configurations, we arrived at the conclusion that a triple-mass lens system is imperative to account for the anomalous features observed in the lensing light curve. Results. From the Bayesian analysis using the measured observables of the event timescale and angular Einstein radius, we determined that the least massive component of the lens has a planetary mass of 4.36_−2.18^+2.35M_J. This planet orbits within a stellar binary system composed of two stars with masses 0.71_−0.36^+0.38M_⊙and 0.56_−0.28^+0.30M_⊙. This lensing event signifies the sixth occurrence of a planetary microlensing system in which a planet belongs to a stellar binary system. 

Aims. The light curves of the microlensing events MOA-2022-BLG-091 and KMT-2024-BLG-1209 exhibit anomalies with very similar features. These anomalies appear near the peaks of the light curves, where the magnifications are moderately high, and are distinguished by weak caustic-crossing features with minimal distortion while the source remains inside the caustic. To achieve a deeper understanding of these anomalies, we conducted a comprehensive analysis of the lensing events. Methods. We carried out binary-lens modeling with a thorough exploration of the parameter space. This analysis revealed that the anomalies in both events are of planetary origin, although their exact interpretation is complicated by different types of degeneracy. In the case of MOA-2022-BLG-091, the main difficulty in the interpretation of the anomaly arises from a newly identified degeneracy related to the uncertain angle at which the source trajectory intersects the planet–host axis. For KMT-2024-BLG-1209, the interpretation is affected by the previously known inner-outer degeneracy, which leads to ambiguity between solutions in which the source passes through either the inner or outer caustic region relative to the planet host. Results. Bayesian analysis indicates that the planets in both lens systems are giant planets with masses about two to four times that of Jupiter, orbiting early K-type main-sequence stars. Both systems are likely located in the Galactic disk at a distance of around 4 kiloparsecs. The degeneracy in KMT-2024-BLG-1209 is challenging to resolve because it stems from intrinsic similarities in the caustic structures of the degenerate solutions. In contrast, the degeneracy in MOA-2022-BLG-091, which occurs by chance rather than from inherent characteristics, is expected to be resolved by the future space based Roman RGES microlensing survey. 

Abstract We report the analysis of four unambiguous planets and one possible planet from the subprime fields (Γ ≤ 1 hr⁻¹) of the 2017 Korea Microlensing Telescope Network (KMTNet) microlensing survey, to complete the KMTNet AnomalyFinder planetary sample for the 2017 subprime fields. They are KMT-2017-BLG-0849, KMT-2017-BLG-1057, OGLE-2017-BLG-0364, and KMT-2017-BLG-2331 (unambiguous), as well as KMT-2017-BLG-0958 (possible). For the four unambiguous planets, the mean planet–host mass ratios,q, are (1.0, 1.2, 4.6, 13) × 10⁻⁴, the median planetary masses are (6.4, 24, 76, 171)M_⊕, and the median host masses are (0.19, 0.57, 0.49, 0.40)M_⊙, respectively, found from a Bayesian analysis. We have completed the Anomaly Finder planetary sample from the first 4 yr of KMTNet data (2016–2019), with 112 unambiguous planets in total, which nearly tripled the microlensing planetary sample. The “sub-Saturn desert” ( $\log q=\left(-3.6,-3.0\right)$) found in the 2018 and 2019 KMTNet samples is confirmed by the 2016 and 2017 KMTNet samples. 

Abstract In 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 areq ∼ 4 × 10⁻³andq ∼ 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. 

Aims. We investigate the 2023 season data from high-cadence microlensing surveys with the aim of detecting partially covered shortterm signals and revealing their underlying astrophysical origins. Through this analysis, we ascertain that the signals observed in the lensing events KMT-2023-BLG-0416, KMT-2023-BLG-1454, and KMT-2023-BLG-1642 are of planetary origin. Methods. Considering the potential degeneracy caused by the partial coverage of signals, we thoroughly investigate the lensing-parameter plane. In the case of KMT-2023-BLG-0416, we have identified two solution sets, one with a planet-to-host mass ratio ofq~ 10⁻²and the other withq~ 6 × 10⁻⁵, within each of which there are two local solutions emerging due to the inner-outer degeneracy. For KMT-2023-BLG-1454, we discern four local solutions featuring mass ratios ofq~ (1.7−4.3) × 10⁻³. When it comes to KMT-2023-BLG-1642, we identified two locals withq~ (6 − 10) × 10⁻³resulting from the inner-outer degeneracy. Results. We estimate the physical lens parameters by conducting Bayesian analyses based on the event time scale and Einstein radius. For KMT-2023-BLG-0416L, the host mass is ~0.6M_⊙, and the planet mass is ~(6.1−6.7)M_Jaccording to one set of solutions and ~0.04M_Jaccording to the other set of solutions. KMT-2023-BLG-1454Lb has a mass roughly half that of Jupiter, while KMT-2023-BLG-1646Lb has a mass in the range of between 1.1 to 1.3 times that of Jupiter, classifying them both as giant planets orbiting mid M-dwarf host stars with masses ranging from 0.13 to 0.17 solar masses. 

Abstract Magnetic cataclysmic variables (CVs) are luminous Galactic X-ray sources, which have been difficult to find in purely optical surveys due to their lack of outburst behavior. The eROSITA telescope on board the Spektr-RG mission is conducting an all-sky X-ray survey and recently released the public eROSITA Final Equatorial Depth Survey (eFEDS) catalog. We crossmatched the eFEDS catalog with photometry from the Zwicky Transient Facility and discovered two new magnetic CVs. We obtained high-cadence optical photometry and phase-resolved spectroscopy for each magnetic CV candidate and found them both to be polars. Among the newly discovered magnetic CVs is eFEDS J085037.2+044359/ZTFJ0850+0443, an eclipsing polar with orbital period P orb = 1.72 hr and WD mass M WD = 0.81 ± 0.08 M ⊙ . We suggest that eFEDS J085037.2+044359/ZTFJ0850+0443 is a low magnetic field strength polar, with B WD ≲ 10 MG. We also discovered a non-eclipsing polar, eFEDS J092614.1+010558/ZTFJ0926+0105, with orbital period P orb = 1.47 hr and magnetic field strength B WD = 36–42 MG. 

We present the analysis of the microlensing event OGLE-2015-BLG-0845, which was affected by both the microlensing parallax and xallarap effects. The former was detected via the simultaneous observations from the ground and Spitzer, and the latter was caused by the orbital motion of the source star in a relatively close binary. The combination of these two effects led to a mass measurement of the lens object, revealing a low-mass ($$0.14 \pm 0.05 \, \mathrm{ M}_{\odot }$$) M dwarf at the bulge distance ($$7.6 \pm 1.0$$ kpc). The source binary consists of a late F-type subgiant and a K-type dwarf of $$\sim 1.2$$ and $$\sim 0.9 \mathrm{ M}_{\odot }$$, respectively, and the orbital period is $$70 \pm 10$$ d. OGLE-2015-BLG-0845 is the first single-lens event in which the lens mass is measured via the binarity of the source. Given the abundance of binary systems as potential microlensing sources, the xallarap effect may not be a rare phenomenon. Our work thus highlights the application of the xallarap effect in the mass determination of microlenses, and the same method can be used to identify isolated dark lenses. 

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. 

Abstract We resolve the multiple images of the binary-lens microlensing event ASASSN-22av using the GRAVITY instrument of the Very Large Telescope Interferometer (VLTI). The light curves show weak binary-lens perturbations, complicating the analysis, but the joint modeling with the VLTI data breaks several degeneracies, arriving at a strongly favored solution. Thanks to precise measurements of the angular Einstein radiusθ_E= 0.724 ± 0.002 mas and microlens parallax, we determine that the lens system consists of two M dwarfs with masses ofM₁= 0.258 ± 0.008M_⊙andM₂= 0.130 ± 0.007M_⊙, a projected separation ofr_⊥= 6.83 ± 0.31 au, and a distance ofD_L= 2.29 ± 0.08 kpc. The successful VLTI observations of ASASSN-22av open up a new path for studying intermediate-separation (i.e., a few astronomical units) stellar-mass binaries, including those containing dark compact objects such as neutron stars and stellar-mass black holes. 

Aims.The United Kingdom Infrared Telescope (UKIRT) microlensing survey was conducted over four years, from 2016 to 2019, with the goal of serving as a precursor to future near-infrared microlensing surveys. Focusing on stars in the Galactic center and utilizing near-infrared passbands, the survey identified approximately one thousand microlensing events, 27 of which displayed anomalies in their light curves. This paper presents an analysis of these anomalous events, aiming to uncover the underlying causes of the observed anomalies. Methods.The events were analyzed under various configurations, considering the potential binarity of both the lens and the source. For 11 events that were additionally observed by other optical microlensing surveys, including those conducted by the OGLE, KMTNet, and MOA collaborations, we incorporated their data into our analysis. Results.Among the reported anomalous events, we revealed the nature of 24 events except for three events, in which one was likely to be a transient variable, and two were difficult to accurately characterize their nature due to the limitations of the available data. We confirmed the binary lens nature of the anomalies in 22 events. Among these, we verified the earlier discovery that the companion in the binary lens system UKIRT11L is a planetary object. Accurately describing the anomaly in UKIRT21 required a model that accounted for the binarity of both the lens and the source. For two events UKIRT01 and UKIRT17, the anomalies could be interpreted using either a binary-source or a binary-lens model. For the UKIRT05, it was found that accounting for higher-order effects induced by the orbit al motions of both Earth and the binary lens was crucial. With the measured microlensing parallax togeter with the angular Einstein radius, the component masses of the UKIRT05 binary lens were determined to beM₁= (1.05 ± 0.20)M_⊙,M₂= (0.36 ± 0.07)M_⊙, and the distance to the lens was found to beD_L= (3.11 ± 0.40) kpc.