Exoplanets, -moons, -comets

KMT-2018-BLG-0029Lb and OGLE-2019-BLG-0960Lb: Mass Measurements for Two Super-Earth Microlensing Planets

By Keith Cowing
Status Report
astro-ph.EP
August 29, 2025
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KMT-2018-BLG-0029Lb and OGLE-2019-BLG-0960Lb: Mass Measurements for Two Super-Earth Microlensing Planets
Keck NIRC2-LGS images of the two events. North is up and East is to the left. The green and red boxes indicate the target and comparison stars, respectively. Insets show zoomed-in views of each star, including the original image and the residuals following PSF subtraction, which are shown on the identical flux scale to facilitate comparison. The gray dotted circles in the residual images show the predicted lens-source separation. — astro-ph.EP

KMT-2018-BLG-0029Lb and OGLE-2019-BLG-0960Lb were the lowest mass-ratio microlensing planets at the time of discovery. For both events, microlensing parallax measurements from the Spitzer Space Telescope implied lens systems that were more distant and massive than those inferred from the ground-based parallax.

Here, we report on the detection of excess flux aligned to the event locations using Keck Adaptive Optics imaging, which is consistent with the expected brightness of main-sequence hosts under the ground-based parallax, but inconsistent with that predicted by Spitzer.

Based on the excess flux, ground-based parallax, and angular Einstein radius, we determine KMT-2018-BLG-0029Lb to be a 4.2±0.5M⊕ planet orbiting a 0.70±0.07M⊙ host at a projected separation of 3.1±0.3 au, and OGLE-2019-BLG-0960Lb to be a 2.0±0.2M⊕ planet orbiting a 0.40±0.03M⊙ host at a projected separation of 1.7±0.1 au. We report on additional light-curve models for KMT-2018-BLG-0029 under the generalized inner-outer (offset) degeneracy, which were not reported in the original analysis.

We point out inconsistencies in the inner/outer labeling of the degenerate models in the lens and source planes, and advocate for the lens-plane convention, which refers to the planet being closer or further to the host star compared to the image it perturbs. Lastly, we discuss the possibility of breaking this degeneracy via ground concurrent observations with the Roman Space Telescope.

Keming Zhang, Sean K. Terry, Joshua S. Bloom, B. Scott Gaudi, Jessica R. Lu

Comments: 11 pages, 5 figures, 2 tables. Accepted to the Astronomical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2508.18343 [astro-ph.EP] (or arXiv:2508.18343v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2508.18343
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Submission history
From: Keming Zhang
[v1] Mon, 25 Aug 2025 18:00:00 UTC (4,984 KB)
https://arxiv.org/abs/2508.18343

Astrobiology

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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