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arxiv: 2605.17053 · v1 · pith:RT52JYAZnew · submitted 2026-05-16 · 🌌 astro-ph.EP · astro-ph.GA· astro-ph.IM

Systematic KMTNet Planetary Anomaly Search. XIII. Complete Sample of 2021 Prime Field Planets

In-Gu Shin , Jennifer C. Yee , Weicheng Zang , Cheongho Han , Andrew Gould , Shude Mao , Chung-Uk Lee , Yoon-Hyun Ryu
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Ian A. Bond Takahiro Sumi Michael D. Albrow Sun-Ju Chung Kyu-Ha Hwang Youn Kil Jung Yossi Shvartzvald Hongjing Yang Sang-Mok Cha Dong-Jin Kim Seung-Lee Kim Dong-Joo Lee Yongseok Lee Byeong-Gon Park Richard W. Pogge Fumio Abe David P. Bennett Aparna Bhattacharya Ryusei Hamada Yuki Hirao Stela Ishitani Silva Shota Miyazaki Yasushi Muraki Kansuke NUNOTA Greg Olmschenk Cl'ement Ranc Nicholas J. Rattenbury Yuki K. Satoh Daisuke Suzuki Takuto Tamaoki Sean K. Terry Paul. J. Tristram Aikaterini Vandorou Hibiki Yama
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Pith reviewed 2026-05-20 15:28 UTC · model grok-4.3

classification 🌌 astro-ph.EP astro-ph.GAastro-ph.IM
keywords microlensing planetsKMTNet surveyexoplanet demographicsplanetary anomaliesbulge observations2021 seasonhidden planetary systems
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The pith

A systematic search of 2021 KMTNet prime-field data uncovers seven new planetary systems and three candidates that account for one-third of all microlensing planets found that season.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper applies a systematic anomaly search to the archived 2021 KMTNet high-cadence prime-field observations. It identifies seven previously hidden planetary systems and three planet candidates. These represent roughly 33 percent of the microlensing planets detected in those fields during the bulge season. The result shows that systematic searches recover a substantial fraction of planets missed by standard by-eye methods. A complete sample is required to carry out unbiased statistical studies of planet occurrence rates across the Galaxy.

Core claim

In the 2021 KMTNet Prime fields we identified seven hidden planetary systems and three planet candidates through systematic anomaly search. These new planets represent about 33 percent of the total microlensing planets discovered within the Prime fields observed during the 2021 bulge season. While by-eye search remains the primary channel and accounts for about two-thirds of discoveries, the work shows that systematic searches are still necessary to construct a complete microlensing planet sample essential for unbiased statistical studies of planet demographics in the Galaxy.

What carries the argument

The Systematic KMTNet Planetary Anomaly Search, a semi-machine-based procedure that scans archived high-cadence light curves for planetary perturbations.

If this is right

  • The total microlensing planet sample in the prime fields becomes substantially more complete.
  • Unbiased demographic studies can now include these previously undetected systems.
  • Public release of the light-curve datasets permits independent verification and additional modeling by other groups.
  • The same systematic approach can be applied to later seasons to continue building the sample.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Extending the method to non-prime fields or other microlensing surveys could reveal additional hidden planets.
  • A fuller sample would allow sharper comparisons of microlensing planet frequencies with those measured by transit and radial-velocity surveys.
  • Future wide-field surveys might adopt systematic anomaly searches as routine to reduce incompleteness.

Load-bearing premise

The light-curve anomalies must be planetary perturbations rather than stellar variability, binary effects, or instrumental artifacts.

What would settle it

Independent re-modeling of any of the seven claimed events that yields no acceptable planetary solution or follow-up data that rules out the planetary interpretation.

Figures

Figures reproduced from arXiv: 2605.17053 by Aikaterini Vandorou, Andrew Gould, Aparna Bhattacharya, Byeong-Gon Park, Cheongho Han, Chung-Uk Lee, Cl'ement Ranc, Daisuke Suzuki, David P. Bennett, Dong-Jin Kim, Dong-Joo Lee, Fumio Abe, Greg Olmschenk, Hibiki Yama, Hongjing Yang, Ian A. Bond, In-Gu Shin, Jennifer C. Yee, Kansuke Nunota, Kyu-Ha Hwang, Michael D. Albrow, Nicholas J. Rattenbury, Paul. J. Tristram, Richard W. Pogge, Ryusei Hamada, Sang-Mok Cha, Sean K. Terry, Seung-Lee Kim, Shota Miyazaki, Shude Mao, Stela Ishitani Silva, Sun-Ju Chung, Takahiro Sumi, Takuto Tamaoki, Weicheng Zang, Yasushi Muraki, Yongseok Lee, Yoon-Hyun Ryu, Yossi Shvartzvald, Youn Kil Jung, Yuki Hirao, Yuki K. Satoh.

Figure 2
Figure 2. Figure 2: πE distributions of KMT-2021-BLG-0424 for APRX inner (u0 > 0; left panel) and (u0 < 0; right panel) cases. The colored dots represent ∆χ 2 ≤ n 2 with respect to the best-fit χ 2 value of each case, where n = 1 (red), 2 (yellow), 3 (green), 4 (light blue), 5 (blue), and 6 (purple). 3.1. KMT-2021-BLG-0424 In [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 4
Figure 4. Figure 4 [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: ξE and πE distributions of KMT-2021-BLG-0690 for XRP and APRX (u0 > 0 and u0 < 0) cases. The color scheme is identical to [PITH_FULL_IMAGE:figures/full_fig_p009_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Σ∆χ 2 plots of KMT-2021-BLG-0690 comparing the APRX and XRP models with their light curves and resid￾uals. The top panel shows the Σ∆χ 2 (APRX − XPR) plot of the whole range of the light curve. The middle panel shows a zoom-in plot around the peak (HJD′ = 9380 to 9390), where the biggest difference between the APRX and XRP models is exhibited. The bottom three panels show the light curve and residuals of t… view at source ↗
Figure 7
Figure 7. Figure 7: Light curve of KMT-2021-BLG-1063 with 2L1S, 1L2S, and 1L1S models. circle for qc = 0.1 and dotted circles for the other qc val￾ues). We find that ξE satisfies a wide range of qc (i.e., from 0.2 to 1.0) within 3σ levels, which implies that this 2L1S XRP model is reasonable. Although the XRP model is more likely than the APRX models, it is difficult to conclude that the XRP model is a fiducial solution of th… view at source ↗
Figure 8
Figure 8. Figure 8: Light curve of KMT-2021-BLG-1691 with 2L1S, 2L2S, 3L1S, and 1L1S models. Because the 2L1S model cannot explain the anoma￾lies, we attempt 3L1S and 2L2S modeling. We find that both interpretations can describe all features of the anomalies as shown in [PITH_FULL_IMAGE:figures/full_fig_p011_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Comparison for 2L2S and 3L1S models of KMT-2021-BLG-1691. ues of the other models are less than 3 compared with the best-fit case, which is insuffient to resolve them. Al￾though these models cannot be resolved, the mass ratios of all models are less than our criterion of planet detec￾tion, i.e., q < 0.03. Thus, all the 2L2S or 3L1S models indicate that at least one of the companions in their lens system is… view at source ↗
Figure 10
Figure 10. Figure 10: Light curve of KMT-2021-BLG-2213 with 2L1S and 1L1S models. 3.6. KMT-2021-BLG-2213 In [PITH_FULL_IMAGE:figures/full_fig_p014_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: Light curve of KMT-2021-BLG-3290 with 2L1S and 1L1S models. (1.803, 1.815, 9421.5, 9393.2, 15.7, 0.216), which is con￾sistent with s+ = 2.259. We find that the 2L1S model indicates that the lens system could have a planet com￾panion (i.e., q ∼ 0.008 ± 0.001). However, the 2L1S model competes with the 1L2S model, which cannot be reliably distinguished from it (∆χ 2 = 7). Because the 2L1S/1L2S degeneracy ca… view at source ↗
Figure 12
Figure 12. Figure 12: Light curve of KMT-2021-BLG-1385 with 2L1S, 1L2S, and 1L1S models. shaped anomaly at HJD′ ∼ 9392.0. We also present the model light curves of 2L1S, 1L2S, and 1L1S mod￾els with their residuals for comparison. We find that the anomaly can be explained by either 2L1S or 1L2S interpretations. We also find that the 2L1S inter￾pretation can describe the anomaly by both small￾and large-ρ∗ cases because the bump … view at source ↗
Figure 14
Figure 14. Figure 14: Light curve of KMT-2021-BLG-1907 with 2L1S, 1L2S, and 1L1S models. 3.10. KMT-2021-BLG-1907 In [PITH_FULL_IMAGE:figures/full_fig_p017_14.png] view at source ↗
Figure 15
Figure 15. Figure 15: Color-magnitude diagrams (CMDs) of plan￾etary events. We use the abbreviation for event names, e.g., KMT-2021-BLG-0424 is abbreviated as KB210424. The HST CMD are presented for visual inspection of the faint sources and are not used for the source-color measurements. For KB210457, KB211063, and KB211691, the CMDs are built by cross-matching with VVV and KMTNet. 4. CMD ANALYSIS Among the seven planetary ev… view at source ↗
Figure 16
Figure 16. Figure 16: Mass-ratio distributions based on various microlensing planet samples. The first sample is from planets discovered in 2016 – 2019 by eye and systematic search series (left-side panels). The second sample includes additional planets from this work and those found by eye in 2021 (middle panels). The third sample includes planets found before the KMTNet survey (2015) and after 2022 (right-side panels). Upper… view at source ↗
read the original abstract

The Systematic KMTNet Planetary Anomaly Search series was conducted using the KMTNet data archived from $2016$ to $2019$. From this first phase of the series, we reported a total of $50$ planetary systems hidden in the data archive, which represent about $35\%$ of the total microlensing planets discovered from $2016$ to $2019$, demonstrating that this semi-machine-based search is a crucial channel for building a complete microlensing planet sample. We continue this series for $2021$ and beyond to expand the microlensing planet sample. In this work for the $2021$ KMTNet high-cadence fields (Prime fields), we find seven hidden planetary systems and three planet candidates. These new planets represent about $33\%$ of the total microlensing planets discovered within the Prime fields observed during the $2021$ bulge season. While the by-eye search is the primary channel for detecting microlensing planets (i.e., two-thirds of microlensing planet discoveries), this work clearly shows that a systematic search series is still necessary for constructing a complete microlensing planet sample. Such a sample is essential for conducting unbiased statistical studies of planet demographics in our Galaxy. Datasets for all the events used for analyses in this work are publicly available.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 2 minor

Summary. The manuscript continues the Systematic KMTNet Planetary Anomaly Search series by analyzing archived 2021 KMTNet Prime field observations. The authors report seven hidden planetary systems and three planet candidates identified via a semi-machine-based search. These represent approximately 33% of the total microlensing planets discovered in the Prime fields during the 2021 bulge season. The work notes that by-eye searches remain the dominant channel (roughly two-thirds of discoveries) but argues that systematic archival searches are still required to assemble a complete sample for unbiased demographic studies. All datasets are released publicly.

Significance. If the classifications hold, the result meaningfully improves the completeness of the microlensing planet catalog, which is essential for statistical studies of Galactic planet demographics. The public data release is a clear strength that enables independent verification and reuse. The stress-test concern about unverified model fits distinguishing planetary perturbations from variability or binaries does not land upon review of the manuscript, because the paper supplies the light-curve modeling details and makes the full datasets available for external checks of residuals and alternative models.

minor comments (2)
  1. The abstract states the 33% figure but does not give the exact total number of planets discovered in the Prime fields; adding this number would make the percentage immediately verifiable.
  2. Notation for 'hidden planetary systems' versus 'planet candidates' should be defined once in the introduction and used consistently thereafter.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their positive assessment of the manuscript and for recommending acceptance. We are pleased that the referee recognizes the value of this systematic search in improving the completeness of the microlensing planet sample and highlights the public data release as a strength.

Circularity Check

0 steps flagged

No significant circularity: direct empirical counts from observational data.

full rationale

The paper reports counts of seven hidden planetary systems and three candidates identified via systematic search of KMTNet light curves, representing 33% of 2021 Prime-field planets. These are observational tallies, not outputs of equations or models that reduce by construction to the paper's own inputs or fitted parameters. No self-definitional steps, fitted inputs renamed as predictions, or load-bearing self-citations appear in the provided text; the central result is a straightforward percentage of detected events. The work is self-contained against external benchmarks of microlensing planet discovery rates.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The paper relies on established microlensing event modeling and standard data reduction pipelines from the KMTNet survey without introducing new free parameters or postulated entities.

axioms (1)
  • domain assumption Microlensing light curves can be modeled to distinguish planetary perturbations from other variability sources.
    Invoked when classifying anomalies as planetary; standard assumption in the microlensing field.

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