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Adaptive optics imaging can break the central caustic cusp approach degeneracy in high-magnification microlensing events


Terry, SK and Bennett, DP and Bhattacharya, A and Koshimoto, N and Beaulieu, J and Blackman, JW and Bond, IA and Cole, AA and Lu, JR and Marquette, JB and Ranc, C and Rektsini, N and Vandorou, A, Adaptive optics imaging can break the central caustic cusp approach degeneracy in high-magnification microlensing events, The Astronomical Journal, 164, (5) Article 217. ISSN 0004-6256 (2022) [Refereed Article]

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2022. The Authors. Published by the American Astronomical Society. This article is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) License (, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

DOI: doi:10.3847/1538-3881/ac9518


We 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 ${M}_{{\rm{A}}}={1.12}_{-0.09}^{+0.11}$ and ${M}_{{\rm{B}}}={0.47}_{-0.10}^{+0.13}\,{M}_{\odot }$ 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 Details

Item Type:Refereed Article
Keywords:gravitational microlensing, binary stars, galactic bulge
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Stellar astronomy and planetary systems
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Beaulieu, J (Dr Jean-Philippe Beaulieu)
UTAS Author:Blackman, JW (Mr Joshua Blackman)
UTAS Author:Cole, AA (Professor Andrew Cole)
UTAS Author:Rektsini, N (Mrs Efstathia Natalia Rektsini)
ID Code:154128
Year Published:2022
Funding Support:Australian Research Council (DP200101909)
Deposited By:Physics
Deposited On:2022-11-01
Last Modified:2023-01-10

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