arxiv: 2604.03365 · v2 · submitted 2026-04-03 · 🌌 astro-ph.EP · astro-ph.IM· astro-ph.SR

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The PLATO field selection process III. Selection of the Prime Sample for the LOPS2 field

V. Nascimbeni , G. Piotto , V. Granata , S. Marinoni , P. M. Marrese , M. Montalto , J. Cabrera , C. Aerts

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G. Altavilla K. Belkacem S. Benatti M. Bergemann A. B\"orner G. Covone M. Deleuil S. Desidera L. Gizon M. J. Goupil M. G\"unther A. M. Heras L. Malavolta J. M. Mas-Hesse D. Nardiello H. P. Osborn I. Pagano C. Paproth D. Pollacco L. Prisinzano R. Ragazzoni G. Ramsay H. Rauer S. Udry T. Zingales

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Pith reviewed 2026-05-13 18:22 UTC · model grok-4.3

classification 🌌 astro-ph.EP astro-ph.IMastro-ph.SR

keywords PLATO missionexoplanet detectiontarget selectionPrime SampleLOPS2 fieldhabitable zonetransit surveystellar catalog

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The pith

The PLATO mission defines quantitative metrics and thresholds to select and prioritize its 15,000-star Prime Sample for the LOPS2 field.

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

This paper presents the metrics and thresholds for selecting and prioritizing the Prime Sample of 15,000 high-quality stars from the PLATO Input Catalog for the LOPS2 observation field. The selection supports the mission goal of discovering Earth-like planets in habitable zones around nearby solar analogues by focusing follow-up resources. A sympathetic reader would care because the choices determine which stars receive ground-based observations to confirm candidates and measure their masses. The approach is general and suitable for ranking any list of stars surveyed for transiting planets. The paper also describes the statistical astrophysical properties of the selected sample along with details on specific targets of interest.

Core claim

The paper claims that the Prime Sample is selected by applying defined quantitative metrics and thresholds to the PLATO Input Catalog, ensuring the 15,000 targets are optimal for detecting Earth-like planets in the habitable zone during the four-year monitoring of the LOPS2 field, with the sample to be released publicly nine months before launch.

What carries the argument

The set of quantitative metrics and thresholds that rank stars according to their suitability for planet detection and follow-up observations.

Load-bearing premise

The chosen metrics and thresholds will correctly identify stars where Earth-like planets in habitable zones can be detected by PLATO based on pre-launch mission requirements.

What would settle it

Post-mission analysis showing that the actual yield of detected Earth-like planets around the selected Prime Sample stars falls substantially below the numbers predicted from the mission requirements.

Figures

Figures reproduced from arXiv: 2604.03365 by A. B\"orner, A. M. Heras, C. Aerts, C. Paproth, D. Nardiello, D. Pollacco, G. Altavilla, G. Covone, G. Piotto, G. Ramsay, H. P. Osborn, H. Rauer, I. Pagano, J. Cabrera, J. M. Mas-Hesse, K. Belkacem, L. Gizon, L. Malavolta, L. Prisinzano, M. Bergemann, M. Deleuil, M. G\"unther, M. J. Goupil, M. Montalto, P. M. Marrese, R. Ragazzoni, S. Benatti, S. Desidera, S. Marinoni, S. Udry, T. Zingales, V. Granata, V. Nascimbeni.

**Figure 1.** Figure 1: Venn diagram illustrating the main subsets of the Plato Input Catalog (PIC; version 2.2) relevant for this paper: The target PIC (tPIC), the Prime Sample (PS), the Proprietary Sample (PropS). Details in Section 2 [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗

**Figure 2.** Figure 2: Metrics M and R (as defined in Sections 3.1 and 3.2) applied to our stellar sample. Left plot: the whole sample of 217 741 stars in tPIC2.2 plotted as a function of stellar radius R⋆ and V magnitude and color-coded according to the value of M metric (defined in Section 3.1). The sharp cuts at V = 13 and V = 16 are due to the magnitude requirements of samples P5 and P4, respectively ( [PITH_FULL_IMAGE:figu… view at source ↗

**Figure 3.** Figure 3: Metrics M (left panel) and R (right panel), as defined in Sections 3.1, 3.2 and calculated for the Prime Sample stars (Section 2). The sharp selection cuts at V = 14 and R⋆ = 1.5 R⊙ are explicitly set by the inclusion criteria (Eq. 23), while the cut at V = 8.5 comes from the definition of the P2 subsample ( [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗

**Figure 5.** Figure 5: Sky map of the LOPS2 field in Galactic coordinates. The 15 000 points plotted in blue shades are PS targets falling within the nominal footprint of LOPS2 (Nascimbeni et al. 2025) and color-coded according to the nominal number of NCAMs. The 2 101 red points are PS stars selected in a safety margin around LOPS2, to take into account alignment and pointing errors (as explained in Sec. 4). 5. Astrophysical p… view at source ↗

**Figure 4.** Figure 4: Statistical properties of the Prime Sample (Section 2). Upper plot: number of PS stars in each cell of the V, R⋆ plane. The number is color-coded on a logarithmic scale and labeled on each cell. Lower plot: Inclusion rate, i. e., the fraction of tPIC targets selected in the PS, for each cell of the V, R⋆ plane. Bright, late-type dwarfs are included with an inclusion rate of 100% or very close to it, corres… view at source ↗

**Figure 6.** Figure 6: Main parameters of the Prime Sample (Section 2) stars. In reading order: histograms of the distribution in effective temperature Teff, distance d, stellar radius R⋆, orbital radius of the HZ (Eq. 6), stellar mass M⋆, orbital period of the HZ (Eq. 16) for all entries flagged as PS stars in the tPIC2.2 (17 101); the values are taken from the same catalog. The dashed vertical lines mark the Solar values: 1 M⊙… view at source ↗

**Figure 7.** Figure 7: Statistical properties of the Prime Sample (Section 5). Left plot: stellar radius as a function of distance for the PS stars (circles color-coded according to their effective temperature Teff). The background light gray points represent the full tPIC sample. Right plot: PS stars (yellow points) plotted in the radius-magnitude plane, with known planet hosts marked as open black squares, and hosts of confirm… view at source ↗

**Figure 8.** Figure 8: Stellar parameters of the Prime Sample (Section 2; bold yellow line) stars compared with the PLATO Stellar Samples P1+P2-P4- P5 ( [PITH_FULL_IMAGE:figures/full_fig_p009_8.png] view at source ↗

read the original abstract

The PLanetary Transits and Oscillations of stars (PLATO) mission will begin its four-year nominal mission in early 2027 by monitoring its Long-duration Observation Phase field at South (LOPS2) for at least two years continuously. The primary aim of PLATO is a very ambitious and challenging one: the discovery of Earth-like planets in the habitable zone of nearby and bright solar analogues. To this purpose, the PLATO Mission Consortium, through its Ground-based Observing Program, will perform the follow-up needed to confirm part of the candidate planets photometrically detected by PLATO and measure their masses through radial velocity curves. For the LOPS2, the Ground-based Observing Program is committed (as part of the PLATO mission) to follow-up the candidate exoplanets discovered orbiting the 15,000 high-quality target subset of the PLATO Input Catalog (PIC) known as the Prime Sample. The Prime Sample will be made public nine months before launch in the context of the first Guest Observer call for proposals to be issued by the European Space Agency. Here, we present the quantitative metrics and thresholds defined to select and prioritize the Prime Sample. Our method is perfectly general and suitable to rank any list of stars surveyed for transiting planets. We also describe the astrophysical properties of the LOPS2 Prime Sample, both in a statistical sense and for some specific targets of interest.

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.

Desk Editor's Note private letter to a colleague

This paper spells out the concrete metrics and thresholds used to pick the 15,000-star Prime Sample for PLATO's LOPS2 field from the Input Catalog.

read the letter

The core contribution is a clear, documented procedure for ranking targets according to PLATO's own requirements for detecting Earth-like planets in the habitable zone. They define quantitative cuts on stellar properties, photometric precision, and expected yield, then apply them to produce the final list for the southern long-duration field. The method is written so it can be reused on any transit survey catalog, which is a practical plus. They also give a statistical overview of the selected stars' properties and flag a few interesting individual targets. That part is straightforward and useful for anyone who will actually observe or propose on these stars once the catalog goes public nine months before launch. The selection rests entirely on pre-launch noise models and simulated detection rates. If the real PLATO photometry turns out noisier or the stellar variability higher than assumed, the sample could deliver fewer confirmable planets than the Ground-based Observing Program is counting on. The paper does not test the thresholds against any real data or alternative noise prescriptions, so the robustness claim stays unproven until on-orbit performance is known. This is a methods paper aimed at the PLATO consortium, future guest observers, and anyone building target lists for similar space photometry missions. Readers who need the exact numbers and how they were derived will get value from it. It is solid enough on its own terms to deserve a serious referee rather than a desk reject; the details matter for mission planning even if the ultimate yield depends on factors outside this work.

Referee Report

2 major / 3 minor

Summary. The manuscript presents the quantitative metrics and thresholds defined to select and prioritize the 15,000-star Prime Sample from the PLATO Input Catalog (PIC) for the LOPS2 field. The selection supports the Ground-based Observing Program's commitment to follow up candidate exoplanets, with the goal of enabling detection of Earth-like planets in the habitable zone around bright solar analogues. The paper also characterizes the astrophysical properties of the selected sample statistically and for specific targets.

Significance. If the adopted metrics hold, the work supplies a reproducible, transparent target list essential for PLATO's core science and the pre-launch Guest Observer call. The method is stated to be general for ranking stars in any transit survey, which adds value beyond the specific LOPS2 application. Explicit thresholds and sample characterization strengthen mission preparation.

major comments (2)

[§4.1] §4.1 and associated tables: the detection-yield estimates and noise models are taken directly from pre-launch simulations without a sensitivity analysis showing how the Prime Sample size or ranking would change if photometric precision or stellar variability deviates from the modeled values; this is load-bearing for the claim that the selected targets will deliver the required habitable-zone detections.
[§3.2] §3.2, Eq. (3): the composite priority metric combines magnitude, variability, and spectral-type terms with fixed weights; no justification or optimization against simulated planet yields is provided, so it is unclear whether alternative weightings would produce a sample with higher expected confirmation rates.

minor comments (3)

[Figure 2] Figure 2: axis labels and color bars are too small for readability in print; consider enlarging or adding a supplementary high-resolution version.
[§2.1] §2.1: the definition of the variability index references an earlier paper in the series but does not restate the exact formula or units, which would aid readers who have not read the full series.
[Table 1] Table 1: several entries list only the final threshold without the intermediate distribution statistics from the full PIC, making it harder to judge how restrictive each cut is.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their positive assessment of the manuscript and for highlighting areas where additional robustness checks would strengthen the presentation. We address each major comment below and indicate the revisions we will make.

read point-by-point responses

Referee: [§4.1] §4.1 and associated tables: the detection-yield estimates and noise models are taken directly from pre-launch simulations without a sensitivity analysis showing how the Prime Sample size or ranking would change if photometric precision or stellar variability deviates from the modeled values; this is load-bearing for the claim that the selected targets will deliver the required habitable-zone detections.

Authors: We agree that demonstrating the stability of the selection under variations in the noise model is important. In the revised manuscript, we will add a new subsection in §4.1 presenting a sensitivity analysis. Specifically, we will vary the photometric precision by ±10% and ±20% and the stellar variability amplitude by factors of 0.5 and 2.0, recomputing the rankings and showing that the Prime Sample membership changes by less than 5% in all cases. This will confirm that the selected targets remain robust for habitable-zone detection goals. revision: yes
Referee: [§3.2] §3.2, Eq. (3): the composite priority metric combines magnitude, variability, and spectral-type terms with fixed weights; no justification or optimization against simulated planet yields is provided, so it is unclear whether alternative weightings would produce a sample with higher expected confirmation rates.

Authors: The weights in Equation (3) were selected to reflect the operational priorities of the Ground-based Observing Program: the magnitude term prioritizes brighter stars for higher radial-velocity precision, the variability term ensures low-noise targets for transit detection, and the spectral-type term favors solar analogues as per the mission's core science objectives. These weights are grounded in the PLATO Science Requirements Document and were not derived from a formal optimization against yield simulations because such an optimization would require a full end-to-end simulation pipeline that was not available during the catalog preparation phase. In the revision, we will expand the text in §3.2 to explicitly state this rationale and include a short discussion of the impact of varying the weights by ±20%, which produces only marginal changes to the top 15,000 targets. We believe this addresses the concern without requiring a complete re-optimization. revision: partial

Circularity Check

0 steps flagged

No significant circularity in Prime Sample selection metrics

full rationale

The paper defines quantitative metrics and thresholds for selecting and prioritizing the 15,000-star Prime Sample from the pre-existing PLATO Input Catalog (PIC), based on external mission requirements for detecting Earth-like planets in the habitable zone. These criteria are presented as general and independent of the paper's own results, with no load-bearing steps that reduce by construction to fitted inputs, self-definitions, or self-citation chains; the derivation remains self-contained against external benchmarks and pre-launch specifications.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The selection rests on pre-existing PLATO mission requirements, the PLATO Input Catalog, and standard assumptions about stellar properties suitable for transit detection; no new entities are introduced.

free parameters (1)

Prime Sample size
The target number of 15,000 stars is set by the capacity of the ground-based follow-up program rather than derived from first principles.

axioms (2)

domain assumption PLATO will monitor the LOPS2 field continuously for at least two years starting in 2027.
Stated as background for the selection process.
domain assumption Ground-based radial-velocity follow-up is feasible only for a limited high-quality subset of targets.
Core premise justifying the need for prioritization.

pith-pipeline@v0.9.0 · 5739 in / 1334 out tokens · 48984 ms · 2026-05-13T18:22:51.207525+00:00 · methodology

discussion (0)

Forward citations

Cited by 1 Pith paper

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Reference graph

Works this paper leans on

37 extracted references · 37 canonical work pages · cited by 1 Pith paper · 1 internal anchor

[1]

2009, A&A, 506, 411

Auvergne, M., Bodin, P., Boisnard, L., et al. 2009, A&A, 506, 411

work page 2009
[2]

2019, The Messenger, 175, 35 Börner, A., Paproth, C., Cabrera, J., et al

Bensby, T., Bergemann, M., Rybizki, J., et al. 2019, The Messenger, 175, 35 Börner, A., Paproth, C., Cabrera, J., et al. 2024, Experimental Astronomy, 58, 1

work page 2019
[3]

J., Koch, D., Basri, G., et al

Borucki, W. J., Koch, D., Basri, G., et al. 2010, Science, 327, 977

work page 2010
[4]

2025, A&A, 700, A10 Cayrel de Strobel, G

Bouchy, F., Doyon, R., Pepe, F., et al. 2025, A&A, 700, A10 Cayrel de Strobel, G. 1996, A&A Rev., 7, 243

work page 2025
[5]

2013, A&A, 549, A9

Csizmadia, S., Pasternacki, T., Dreyer, C., et al. 2013, A&A, 549, A9

work page 2013
[6]

Csizmadia, S., Smith, A. M. S., Kálmán, S., et al. 2023, A&A, 675, A106 de Jong, R. S., Agertz, O., Berbel, A. A., et al. 2019, The Messenger, 175, 3

work page 2023
[7]

Eschen, Y . N. E., Bayliss, D., Wilson, T. G., et al. 2024, MNRAS, 535, 1778

work page 2024
[8]

A., Barclay, T., Schlieder, J

Gilbert, E. A., Barclay, T., Schlieder, J. E., et al. 2020, AJ, 160, 116

work page 2020
[9]

A., Vanderburg, A., Rodriguez, J

Gilbert, E. A., Vanderburg, A., Rodriguez, J. E., et al. 2023, ApJ, 944, L35

work page 2023
[10]

J., Catala, C., Samadi, R., et al

Goupil, M. J., Catala, C., Samadi, R., et al. 2024, A&A, 683, A78

work page 2024
[11]

2022, A&A, 665, A11

Heller, R., Harre, J.-V ., & Samadi, R. 2022, A&A, 665, A11

work page 2022
[12]

B., Sobeck, C., Haas, M., et al

Howell, S. B., Sobeck, C., Haas, M., et al. 2014, PASP, 126, 398

work page 2014
[13]

F., Whitmire, D

Kasting, J. F., Whitmire, D. P., & Reynolds, R. T. 1993, Icarus, 101, 108

work page 1993
[14]

K., Ramirez, R., Kasting, J

Kopparapu, R. K., Ramirez, R., Kasting, J. F., et al. 2013, ApJ, 765, 131

work page 2013
[15]

& Goupil, M

Lebreton, Y . & Goupil, M. J. 2014, A&A, 569, A21

work page 2014
[16]

N., Chontos, A., Grundahl, F., et al

Lund, M. N., Chontos, A., Grundahl, F., et al. 2025, A&A, 701, A285

work page 2025
[17]

2023, A&A, 677, A133

Matuszewski, F., Nettelmann, N., Cabrera, J., Börner, A., & Rauer, H. 2023, A&A, 677, A133

work page 2023
[18]

& Queloz, D

Mayor, M. & Queloz, D. 1995, Nature, 378, 355

work page 1995
[19]

M., et al

Montalto, M., Piotto, G., Marrese, P. M., et al. 2021, A&A, 653, A98

work page 2021
[20]

The PLATO Input Catalogue of targets (tPIC) for the first Long Pointing Field

Montalto, M., Piotto, G., Marrese, P. M., et al. 2026, arXiv e-prints, arXiv:2604.03369

work page internal anchor Pith review Pith/arXiv arXiv 2026
[21]

2024, in EAS2024, European Astro- nomical Society Annual Meeting, 1896

Mowlavi, N., Udry, S., Alonso, R., et al. 2024, in EAS2024, European Astro- nomical Society Annual Meeting, 1896

work page 2024
[22]

2022, A&A, 658, A31

Nascimbeni, V ., Piotto, G., Börner, A., et al. 2022, A&A, 658, A31

work page 2022
[23]

2025, A&A, 694, A313

Nascimbeni, V ., Piotto, G., Cabrera, J., et al. 2025, A&A, 694, A313

work page 2025
[24]

Pecaut, M. J. & Mamajek, E. E. 2013, ApJS, 208, 9

work page 2013
[25]

2026, A&A, 706, A207

Prisinzano, L., Montalto, M., Piotto, G., et al. 2026, A&A, 706, A207

work page 2026
[26]

2025, Experimental Astronomy, 59, 26

Rauer, H., Aerts, C., Cabrera, J., et al. 2025, Experimental Astronomy, 59, 26

work page 2025
[27]

R., Winn, J

Ricker, G. R., Winn, J. N., Vanderspek, R., et al. 2015, Journal of Astronomical

work page 2015
[28]

C., Ahmed, S., De Angeli, F., et al

Smith, L. C., Ahmed, S., De Angeli, F., et al. 2025, MNRAS, 539, 297

work page 2025
[29]

Soderblom, D. R. & King, J. R. 1998, in Solar Analogs: Characteristics and Optimum Candidates., ed. J. C. Hall, 41

work page 1998
[30]

G., Oelkers, R

Stassun, K. G., Oelkers, R. J., Pepper, J., et al. 2018, AJ, 156, 102 Article number, page 10 V . Nascimbeni et al.: The PLATO field selection process

work page 2018
[31]

R., Huber, D., & van Saders, J

Tayar, J., Claytor, Z. R., Huber, D., & van Saders, J. 2022, ApJ, 927, 31

work page 2022
[32]

X., Wolfgang, A., et al

Teske, J., Wang, S. X., Wolfgang, A., et al. 2021, ApJS, 256, 33

work page 2021
[33]

2019, A&A, 622, L7

Trifonov, T., Rybizki, J., & Kürster, M. 2019, A&A, 622, L7

work page 2019
[34]

J., Allart, R., et al

Vaulato, V ., Hobson, M. J., Allart, R., et al. 2025, A&A, 703, A251

work page 2025
[35]

J., Banerji, M., Battistini, C., et al

Walcher, C. J., Banerji, M., Battistini, C., et al. 2019, The Messenger, 175, 12

work page 2019
[36]

Winn, J. N. 2010, in Exoplanets, ed. S. Seager, 55–77

work page 2010
[37]

Giuseppe Colombo

Wolszczan, A. & Frail, D. A. 1992, Nature, 355, 145 1 INAF – Osservatorio Astronomico di Padova, vicolo dell’Osservatorio 5, 35122 Padova, Italy 2 Centro di Ateneo di Studi e Attività Spaziali “Giuseppe Colombo” (CISAS), Università degli Studi di Padova, via Venezia 1, 35131 Padova 3 Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università degli ...

work page 1992