OGLE-2015-BLG-0845L: A low-mass M dwarf from the microlensing parallax and xallarap effects
Authors: Zhecheng Hu, Wei Zhu, Andrew Gould, Andrzej Udalski, Takahiro Sumi, Ping Chen, Sebastiano Calchi Novati, Jennifer C. Yee, Charles A. Beichman, Geoffery Bryden, Sean Carey, Michael Fausnaugh, B. Scott Gaudi, Calen B. Henderson, Yossi Shvartzvald, Benjamin Wibking, Przemek Mróz, Jan Skowron, Radoslaw Poleski, Michaeł K. Szymański, Igor Soszynśki, Paweł Pietrukowicz, Szymon Kozłowski, Krzysztof Ulaczyk, Krzysztof A. Rybicki, Patryk Iwanek, Marcin Wrona, Mariusz Gromadzki, Fumio Abe, Richard Barry, David P. Bennett, Aparna Bhattacharya, Ian A. Bond, Hirosane Fujii, Akihiko Fukui, Ryusei Hamada, Yuki Hirao, Stela Ishitani Silva, Yoshitaka Itow, Rintaro Kirikawa, Naoki Koshimoto, Yutaka Matsubara, Shota Miyazaki, Yasushi Muraki, Greg Olmschenk, Clément Ranc, Nicholas J. Rattenbury, Yuki Satoh, Daisuke Suzuki, Mio Tomoyoshi, Paul. J. Tristram, Aikaterini Vandorou, Hibiki Yama, Kansuke Yamashita
Abstract
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 direct mass measurement of the lens object, revealing a low-mass ($0.14 \pm 0.05 M_{\odot}$) 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 $\sim1.2 M_{\odot}$ and $\sim 0.9 M_{\odot}$, respectively, and the orbital period is $70 \pm 10$ days. 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.
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OGLE-2019-BLG-0825: Constraints on the Source System and Effect on Binary-lens Parameters Arising from a Five-day Xallarap Effect in a Candidate Planetary Microlensing EventY. Satoh, N. Koshimoto, D. Bennett et al. · 2023 · Astronomical Journal · cited 2 times · Not summarized yet
Abstract
We present an analysis of microlensing event OGLE-2019-BLG-0825. This event was identified as a planetary candidate by preliminary modeling. We find that significant residuals from the best-fit static binary-lens model exist and a xallarap effect can fit the residuals very well and significantly improves χ 2 values. On the other hand, by including the xallarap effect in our models, we find that binary-lens parameters such as mass ratio, q, and separation, s, cannot be constrained well. However, we also find that the parameters for the source system such as the orbital period and semimajor axis are consistent between all the models we analyzed. We therefore constrain the properties of the sou…
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OGLE-2015-BLG-1395Lb: A Cold Sub-Saturn Mass Planet Orbiting an M DwarfAndrew A. Cole, Joshua W. Blackman, Jean-Philippe Beaulieu et al. · 2026 · Earth and Planetary Astrophysics · AI summary available
In short
Microlensing and adaptive-optics observations reveal a cold sub-Saturn orbiting a low-mass M dwarf, with physical parameters sharpened by uncertain Spitzer parallax constraints.
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OGLE-2016-BLG-0523: A Low-mass Brown Dwarf or Super-Jupiter in a >100 au OrbitHong-Jing Yang, W. Zang, Y. Ryu et al. · 2026 · Astrophysical Journal Letters · Not summarized yet
Abstract
To search for very wide-orbit binary-lens events, we crossmatch microlensing events detected by the Optical Gravitational Lensing Experiment (OGLE)-IV and KMTNet between 2011 and 2024. After removing contaminants from variable stars, we identify OGLE-2016-BLG-0523 as a microlensing event showing two short-lived bumps in its light curve, with the two separated by 8.36 yr. We investigate three scenarios to explain the two bumps, including a binary-lens single-source (2L1S), a single-lens binary-source (1L2S), and two unrelated single-lens single-source events (2×1L1S). The 1L2S interpretation is excluded due to its poorer fit to the data, while the 2×1L1S scenario is disfavored by the low even…
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Two Low-Mass-Ratio Microlensing Planets from High-Magnification Events: KMT-2021-BLG-0247 and MOA-2023-BLG-169K. Nunota, A. Gould, T. Sumi et al. · 2026 · Not summarized yet
Abstract
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 $M_{\rm L}=0.9\pm0.1\,M_\odot$ and $D_{\rm L}=6.7^{+1.0}_{-0.3}\,\mathrm{kpc}$, respectively, and the planet mass is $M_{\rm p}=41\pm5\,M_\oplus$. The projected planet--host separations are $a_\perp=3.4^{+0.7}_{-0.3}\,\mathrm{au}…
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A Search For Stellar-mass Black Holes Via Astrometric Microlensing II: 2012-2015 Keck CandidatesMace J. Huston, Jessica R. Lu, Casey Y. Lam et al. · 2026 · Not summarized yet
Abstract
The Milky Way is expected to host $\sim$10$^8$ stellar-mass black holes with an uncertain binary fraction. The only proven method to detect isolated stellar mass black holes is gravitational microlensing. Here we report the results of a microlensing search for black holes with photometry and astrometry. By combining 10 years of seeing-limited photometry from OGLE and MOA with diffraction-limited photometry and astrometry from adaptive optics imagers at the W.~M.~Keck Observatory, we constrain lens masses for OGLE-2012-BLG-0169, OGLE-2014-BLG-0613/MOA-2015-BLG-041, OGLE-2015-BLG-0029/MOA-2015-BLG-170, and OGLE-2015-BLG-0211. Of the four long-duration microlensing events monitored, we ruled ou…
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OGLE-2013-BLG-1125/MOA-2013-BLG-584: Discovery of a gas giant orbiting an M dwarfÉ. Bachelet, M. Hundertmark, V. Bozza et al. · 2026 · Not summarized yet
Abstract
We report the discovery and characterization of a planetary system in the microlensing event OGLE-2013-BLG-1125/MOA-2013-BLG-584. We analyze photometric data from OGLE and MOA surveys, as well as LCO, $\mu$FUN, and Mindstep follow-up telescopes to model the microlensing light curve. We also used data from the Keck II telescope collected in 2018 to obtain additional constraints on the lensing system. We found a Saturn-mass planet of mass $M_{\rm p}=105\pm13 \ M_\oplus$ orbiting a low-mass host star $M_{\rm L}=0.139\pm0.011 \ M_\odot$ at $1.00\pm0.08$ kpc from Earth. This discovery adds to the small sample of giant planets orbiting low-mass stars and provides constraints on planet formation th…
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OGLE-2012-BLG-0563: Relative Proper Motion Constraint from Keck Follow-up finds the correct LensA. Bhattacharya, D. P. Bennett, J. Beaulieu et al. · 2026 · Not summarized yet
Abstract
We present Keck/NIRC2 adaptive optics imaging results of planetary microlensing event OGLE-2012-BLG-0563. We find that the OGLE-2012-BLG-0563L planetary system consists of a 1.12 +/- 0.09 Jupiter-mass planet orbiting a 0.81 +/- 0.04 solar-mass host star at a distance of 5.49 +/- 0.56 kpc from the Sun. This event has a lens-source separation of 23.28 +/- 0.48 mas, which is the smallest lens-source separation measured to date with Keck AO data. We find that the incorrect solution - which identifies the Northeast (NE) star as the source star - is favored if one only considers the discovery paper, the Fukui et al. (2015) solution, or an unconstrained model. However, by performing an image-constr…
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KMT-2026-BLG-0083L: A Two-Jovian-Planet System Orbiting an M Dwarf Discovered by MicrolensingCheongho Han, Chung-Uk Lee, Zhi-Xing Li et al. · 2026 · Publications of the Astronomical Society of the Pacific · Not summarized yet
Abstract
We present the analysis of the microlensing event KMT-2026-BLG-0083, which was independently detected by the KMTNet, OGLE, and PRIME surveys and also monitored by the DREAMS survey. The combined data provide dense coverage of two distinct short-duration anomalies in the light curve that cannot be reproduced by a standard binary-lens model. Independent analyses of the two anomalies indicate that each is produced by a planetary companion to the lens, motivating a triple-lens interpretation. The modeling yields two pairs of degenerate solutions arising from the well-known inner–outer degeneracy, with each pair exhibiting two local solutions depending on whether the source passes above or below …
Papers that cite it
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A Unified Analytic Framework for Microlensing Caustics: Geode Solutions and Hyper-Catalan SignaturesGleb Berloff, N. Berloff · 2025 · Astrophysical Journal · cited 1 time · Not summarized yet
Abstract
We give a preparation-invariant analytic description of image formation near microlensing caustics. After a local Weierstrass preparation at any multiple image (order d ≥ 2), the lens mapping reduces to a single geode variable m satisfying m = U φ(m), where U is a prepared source coordinate and φ is an image-side kernel. The coefficients of m(U) obey closed hyper-Catalan (HC) recurrences, allowing termwise derivatives and truncation control from the characteristic system. We also use the same form for a short HC predictor–corrector: evaluate the series within its certified radius and apply a brief Newton polish near the boundary. We define an HC signature (first nonzero kernel coefficients) …
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