{"id":"26220e5e-73ce-4683-b4b9-dbb81ac6276a","arxiv_id":"2608.11902","paper_version":1,"verdict":"CONDITIONAL","confidence":"HIGH","novelty_score":6.0,"correctness_risk":"low","formal_verification":"none","parameter_count":4,"one_line_summary":"DMPP-7 hosts a confirmed 0.72 Saturn-mass planet at P=4.93 days; HD 67200 and HD 2134 show moderate evidence for 2.7-2.8 day low-mass candidates that remain unconfirmed.","lead":"Radial velocity observations of three quiet stars reveal one strongly confirmed Saturn-mass planet and two smaller planet candidates that may instead be stellar activity. The work adds a precise 4.9-day planet to known demographics and shows how activity modelling can prevent false planet claims.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"DMPP-7b detection may be a fourth rotational harmonic: the ESP kernel in kima is truncated at n_harm=3, so a Prot/4 signal near 4.93 d cannot be modeled as activity and would be misattributed to a planet.","rationale":"The strongest claim is the confirmed planet DMPP-7b. The paper's Bayesian evidence is strong, but the model space for stellar activity is incomplete: the s+leaf ESP kernel used in kima is truncated at n_harm=3, so it cannot represent a fourth rotational harmonic. DMPP-7's rotation period is ~20 d, making Prot/4≈5 d, which is almost exactly the observed 4.93 d period. The authors themselves identify other periods as rotational harmonics (11.8 d as Prot/2; 9.4 d photometric as a harmonic), demonstrating that harmonics are physically relevant for this star, yet they do not test Prot/4 for the planet signal. The lack of correlation with activity indicators is not decisive, as the paper argues that RV–activity correlations are not stationary and may not be linear. The GP would not absorb a fourth harmonic because of the n_harm=3 truncation, so the 'captured by the chosen Gaussian process' premise in the reader's weakest_assumption is the precise point of failure. A straightforward computational test—re-running with higher harmonics—would settle whether the 4.93 d signal is dynamical or a Prot/4 spot harmonic. If the latter, the central detection collapses; if the former, it is confirmed. This is therefore the most load-bearing concern, and it is actionable. The reader's verdict of CONDITIONAL remains appropriate, but the condition should explicitly include this harmonic test.","tokens_in":40939,"tokens_out":10901,"duration_ms":101667,"concrete_test":"Re-run the kima analysis of DMPP-7 with the ESP kernel configured to include at least the fourth harmonic (n_harm=5) or with the standard SEP kernel, which has infinite harmonics. If the GP+planet model still yields BF(Np=1/Np=0)>150 and a 4.93 d Keplerian with K~22 m/s, the planetary interpretation is robust. If instead the GP alone (Np=0) can absorb the 4.93 d variability, or the evidence for the Keplerian drops below the strong threshold, the signal is likely Prot/4, and DMPP-7b should be reclassified as unconfirmed.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that DMPP-7b is a confirmed planet rests on the 4.93 d RV signal being dynamical. The activity GP used in kima employs the s+leaf ESP kernel truncated at n_harm=3, so it can absorb variability at the characteristic period η3 and at η3/2 and η3/3, but not at η3/4. DMPP-7's rotation period is estimated at ~20 d (median 20.4 d; 68.3% range 12.9–28.3 d), so a fourth rotational harmonic would fall at 3.2–7.1 d, comfortably encompassing the observed 4.93 d period. The paper explicitly interprets the 11.8 d and ~9.4 d periodicities as Prot/2 (and related) signals, but never tests whether the strong 4.93 d signal could be a Prot/4 spot harmonic. If stellar spots produce a fourth harmonic, the truncated GP cannot model it, and the signal would necessarily be absorbed by a Keplerian, yielding a spurious planet with large BF. The absence of correlations with BIS, FWHM, SMW and M3 reduces but does not eliminate this possibility, as the authors themselves note that RV–activity correlations are not stationary and may be phase-dependent. Thus the detection is not yet robust against a specific, plausible stellar contamination.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents a radial-velocity analysis of three bright, low-activity stars selected by the Dispersed Matter Planet Project (DMPP), comparing purely Keplerian models with models that include stellar activity via a Gaussian process (GP). For DMPP-7 (HD 118006), the authors claim strong Bayesian evidence for a single short-period giant planet, DMPP-7b, with P = 4.92666 d and m_p sin i = 68.96 M_Earth, based on HARPS and ESPRESSO data and a Bayes factor BF > 4564 in the GP model. A longer 21–22 d period is interpreted as likely stellar rotation, and a second, more tentative 11.8 d signal is not conclusively distinguished from activity. For HD 67200, a GP-only model is strongly favored over the purely dynamical model, with moderate evidence for a 2.67 d Keplerian (m sin i = 2.07 M_Earth). For HD 2134, the paper finds moderate evidence in all models for a 2.78 d Keplerian (m sin i = 2.86 M_Earth), while the 21–32 d signal is associated with tentative FWHM variability. The paper also reports no transit detections in TESS photometry and places DMPP-7b in the transition region between the high-radius population and the Neptunian ridge/savannah.","tokens_in":41273,"tokens_out":5894,"duration_ms":58196,"significance":"If DMPP-7b is confirmed as a planet, it is a precisely characterized Saturn-mass companion (mass uncertainty ~2.4%) on a 4.93 d orbit around a slightly evolved, bright star, adding a useful anchor point for planet formation and migration models. The paper's methodological approach is a strength: it uses nested sampling with the number of Keplerians as a free parameter, computes global model evidences, and jointly models RVs with simultaneous activity indicators using the s+leaf ESP kernel. The two lower-mass candidates are appropriately presented as moderate-evidence detections with explicit caveats that they may be stellar in origin. The explicit comparison of Keplerian and GP models and the discussion of activity-indicator correlations are valuable for interpreting RV surveys of low-activity stars. However, the central claim of a confirmed planet for DMPP-7b depends on the GP's ability to represent all plausible activity signals, which is the focus of the major comment below.","major_comments":[{"comment":"The GP activity model uses the s+leaf ESP kernel with n_harm = 3, so it can represent variability at the characteristic period η3 and at η3/2 and η3/3, but not at η3/4. DMPP-7's rotation period is estimated at a median of 20.4 d with a 68.3% range of 12.9–28.3 d, so a fourth rotational harmonic would fall at 3.2–7.1 d, fully encompassing the 4.93 d orbital period of the claimed planet. The paper interprets the 11.8 d and 9.4 d signals as Prot/2 and related aliases, but it never tests whether the strong 4.93 d signal could be a Prot/4 spot harmonic. If such a harmonic is present, the truncated GP cannot absorb it, and the large Bayes factor BF > 4564 for a Keplerian would be a model artefact. The absence of correlations with BIS, FWHM, SMW, and M3 reduces but does not eliminate this possibility, as the authors themselves note in §4.1.7 that RV–activity correlations are not stationary and may be phase-dependent. I request a robustness test, for example by allowing more harmonics in the GP (n_harm ≥ 4) or including an explicit Prot/4 activity term, or an explicit physical argument for why a Prot/4 harmonic is negligible for this star.","section":"Appendix A / §4.2.5, Table 4"}],"minor_comments":[{"comment":"The text states 'the 4.297d planet candidate parameters' where the context clearly indicates P = 4.927 d; this appears to be a typo.","section":"§4.2.7"},{"comment":"The equilibrium temperature quoted for HD67200b in §5 is Teff = 616 K, which is inconsistent with Teq = 1650 K (AB = 0) or 1475 K (AB = 0.36) listed in Table 3; please correct the number or the definition used.","section":"§5"},{"comment":"The offset parameters are labelled as γp15,p20−15032.84 and γHARPS−36651, which are confusing because the reference value is embedded in the label; recommend defining the zero-point explicitly in the caption.","section":"Table 2 and Table 4"},{"comment":"The phrase 'we allowed for harmonics with 3 : 2 and 3 : 1 amplitude contributions of η3/2 and η3/3' is unclear; consider rewording to indicate that the GP kernel permits relative harmonic amplitudes at η3/2 and η3/3 as controlled by η4.","section":"§4.1.5"}],"recommendation":"major_revision","confidential_remarks":"The paper is well-written and the statistical framework is sound. The single major concern— the inability of the GP kernel to model a Prot/4 harmonic for DMPP-7—directly affects the confirmation claim. If the authors can demonstrate robustness to this specific alternative (e.g., by extending the harmonic order or by an independent activity argument), the claim would be much stronger. The paper appears to be accepted for publication already; my recommendation is independent of that status."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: DMPP-7b is a real detection and worth knowing about; the other two “systems” are still just candidates, and the title oversells them. The paper earns its keep on the strength of the DMPP-7 analysis.\n\nWhat’s new: fresh ESPRESSO data for DMPP-7, a careful nested-sampling comparison between Keplerian and Gaussian-process models, and an explicit supersession of the earlier DMPP-6b/c interpretation of HD 67200. The DMPP-7b signal is robust: K=22.6 m/s, BF>4564 for GP+Np=1 over GP+Np=0, and the parameters barely move between purely Keplerian and GP models. That consistency is the strongest evidence in the paper.\n\nThe modeling is thoughtful. Using Np as a free parameter, fitting RV and activity indicators simultaneously, and honestly labeling the 2.1–2.9 M_Earth signals as moderate evidence are all good practice. The authors also correctly note that RV–activity correlations can be non-stationary, which keeps them from overclaiming what the line-profile non-detections mean.\n\nWhere I push back: the stress-test concern about the ESP kernel truncated at n_harm=3. Because the GP cannot represent a fourth rotational harmonic, a Prot/4 signal near 4.93 d would necessarily be absorbed by a Keplerian. On reading the paper, I think this is a legitimate caveat but not a fatal one. A 22.6 m/s RV signal from spots would be unusually large given the star’s photometric quietness (R_var=546 ppm, no 4.9 d term in TESS), and the HARPS/ESPRESSO phase coherence over a long baseline is not what I’d expect from evolving spots. Still, the authors should test the Prot/4 hypothesis directly—by extending the η3 prior below 10 d or by fitting the activity indicators at 4.93 d. As written, the model comparison alone cannot rule it out.\n\nLesser issues: the title claims “three new exoplanet systems” when the paper itself says only DMPP-7b has strong evidence; the two short-period candidates are correctly framed as unconfirmed and possibly stellar. The data-availability clause (“on reasonable request”) is weak; the kima adaptation is described but no code is released. Minor typos (e.g., “4.297 d” instead of 4.93 d) will be caught in proof.\n\nWho gets value: RV survey folks and anyone working on activity modeling with GPs. The demographic discussion near the Neptunian savannah is fine but not the main draw.\n\nRecommendation: yes, engage with it. A serious referee should ask for the Prot/4 test and a more honest title; neither should change the central detection.","headline":"Solid confirmation of DMPP-7b plus two honest but unconfirmed candidates; title oversells the system count, and the activity-kernel truncation deserves a direct test.","tokens_in":41858,"tokens_out":2947,"would_cite":true,"duration_ms":33157,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"DMPP-7b: a 0.72-Saturn-mass planet confirmed in a 4.93-day orbit around a bright, slightly evolved star.","keywords":["exoplanets","radial velocities","stellar activity","Gaussian processes","Bayesian model comparison","short-period giant planets","Neptunian desert","low-activity stars"],"falsifier":"Continue monitoring DMPP-7's radial velocities across several more stellar rotation cycles while measuring the S-index, line width, and line asymmetry: a dynamical 4.93-day planet must stay phase-coherent with constant amplitude and no matching line-shape variability, whereas a stellar origin should eventually show amplitude or phase drift, a period change, or the same period appearing in the line-shape indicators.","tokens_in":40760,"feed_emoji":"🪐","tokens_out":24427,"duration_ms":217413,"temperature":0.7,"pith_summary":"The paper aims to establish which of three bright, very low-activity stars selected by the Dispersed Matter Planet Project genuinely host close-orbiting planets once stellar activity is modelled rather than assumed away. Its main claim is that DMPP-7 (HD 118006) hosts one confirmed planet: DMPP-7b, a 0.72-Saturn-mass object with minimum mass $m_\\mathrm{p}\\sin i = 69.0\\pm 1.7\\,M_\\oplus$ and period $P = 4.92666 \\pm 0.00030$ d, supported by very strong Bayesian evidence (Bayes factor $>4564$) and consistent across two independent high-precision spectrograph datasets. The paper also argues that allowing for quasi-periodic stellar activity reverses an earlier two-planet claim for HD 67200, leaving only weak-to-moderate evidence for a $2.07\\,M_\\oplus$ candidate at $P = 2.67$ d, and moderate evidence for a $2.86\\,M_\\oplus$ candidate at $P = 2.78$ d around HD 2134. The wider point is methodological: when the number of Keplerian signals is a free parameter inside an activity-aware model, multi-planet claims around quiet stars can be demoted rather than confirmed.","feed_headline":"A 0.72-Saturn-mass planet confirmed in a 4.93-day orbit","feed_subtitle":"Bayesian modelling separates real planets from stellar noise: DMPP-7b confirmed, two candidates pending.","key_machinery":"The mechanism carrying the argument is a joint Bayesian model in which the radial velocities are the sum of an unknown number of Keplerian orbits plus a quasi-periodic Gaussian process representing stellar activity, with activity indicators (the Ca ii H&K S-index, line width, bisector, and line-asymmetry moment) modelled alongside the RVs where they help. The activity kernel is an exponential--sine periodic process with a characteristic period $\\eta_3$, a decay timescale $\\eta_2$, and a tunable harmonic-complexity parameter $\\eta_4$ controlling how much power sits in the rotation period's harmonics; the number of planets $N_\\mathrm{p}$ is itself a sampled quantity, and models are compared by global evidence expressed as Bayes factors. This machinery lets the analysis ask directly whether a candidate signal is better described as another planet or as correlated stellar noise --- the question that separates the confirmed DMPP-7b from the still-tentative HD 67200 and HD 2134 candidates.","core_discovery":"The paper's central claim is that DMPP-7 (HD 118006), a bright, slightly evolved early-G star, hosts a single close-orbiting giant planet. Combining two high-precision spectrograph datasets in a Bayesian model where the number of Keplerians and a quasi-periodic Gaussian-process activity component are both free, the authors find very strong evidence for one planet: DMPP-7b, with minimum mass $m_\\mathrm{p}\\sin i = 68.96^{+1.69}_{-1.66}\\,M_\\oplus$ (about $0.72$ Saturn masses), period $P = 4.92666 \\pm 0.00030$ d, semi-amplitude $K \\approx 22.6$ m s$^{-1}$, and low eccentricity $e \\approx 0.05$ at $0.0607$ AU. The planet parameters are essentially unchanged whether the residual variability is modelled as a second Keplerian or as correlated activity noise, and the evidence for the planet over activity alone exceeds a Bayes factor of 4564. A longer $21$--$22$ d signal cannot be conclusively assigned to a second planet rather than stellar rotation, and the paper prefers the single-planet-plus-activity reading. The same machinery demotes the previously reported two-planet interpretation of HD 67200 in favour of stellar activity, with only weak-to-moderate evidence for a $P = 2.67$ d, $2.07\\,M_\\oplus$ candidate; for HD 2134, all models give moderate evidence for a $P = 2.78$ d, $2.86\\,M_\\oplus$ candidate. No transits are found in the space-based photometry, and DMPP-7b is placed at the transition between the high-radius population and the Neptunian ridge and savannah regions.","pith_inferences":["A systematic re-run of this activity-aware machinery on the remaining DMPP survey stars would show how often purely Keplerian multi-planet claims are demoted; the paper demonstrates the effect for one target but does not quantify the rate across the survey.","The $2.78$ d HD 2134 signal sits just above the typical supergranulation timescale; if future data show its coherence breaking, convective jitter could mimic ultra-short-period planets of a few $M_\\oplus$ in quiet stars, implying some published masses in this regime are systematically optimistic.","DMPP-7b's predicted radius ($\\approx 9.6\\,R_\\oplus$) lies on the steep part of the mass--radius relation; a single well-timed transit or any direct inclination measurement would test whether the relation holds at exactly this mass.","The success of jointly modelling RVs with the S-index for HD 67200 suggests that future RV campaigns on quiet stars should collect simultaneous activity-indicator timeseries by design, since the rotation signal needed to separate spots from planets is otherwise badly undersampled."],"forward_implications":["A bright ($V = 8.8$), nearby star hosts a short-period giant whose minimum mass is measured to about 2.4%, making DMPP-7b a strong target for atmospheric, orbital, and formation follow-up.","DMPP-7b's low eccentricity at the edge of the Neptunian ridge and savannah favours disc migration over high-eccentricity (Kozai--Lidov) migration as the origin of close-in giants.","For HD 67200, the earlier two-planet claim (DMPP-6b/c) is superseded: activity modelling changes the inferred architecture, so previously announced multi-planet systems around very quiet stars should be re-examined with the same machinery.","If the HD 67200 and HD 2134 short-period signals are confirmed as planets, they would be $2.07$ and $2.86\\,M_\\oplus$ objects on 2.67 d and 2.78 d orbits, hot enough ($\\approx 1500$--$1650$ K) that the paper argues magma-ocean or wind-driven mass loss could supply the dispersed matter the survey was designed to find.","The absence of transits despite a target-selection bias toward near-edge-on orbits implies inclinations below roughly $82^\\circ$--$83^\\circ$ if the photometry is not the limiting factor."],"supporting_citations":[{"why":"Supplies the template-matching reduction that re-extracts the spectrograph radial velocities and activity indicators used throughout; the analysis inherits its precision from this step.","marker":"Silva et al. 2022"},{"why":"Provides the Bayesian modelling tool that treats the number of Keplerian signals as a free parameter and returns global evidences for model comparison.","marker":"Faria et al. 2018, 2023"},{"why":"Implements the diffusive nested sampling algorithm from which the posterior samples and evidence values (including the reported Bayes factors) are drawn.","marker":"Brewer & Foreman-Mackey 2016"},{"why":"Defines the exponential--sine periodic kernel used to model quasi-periodic stellar activity jointly with the RVs and activity indicators.","marker":"Delisle et al. 2020"},{"why":"The prior survey analysis whose single-instrument DMPP-7b solution and purely Keplerian completeness framework this paper extends with a Gaussian process and additional data.","marker":"S26"},{"why":"Describes the second high-precision spectrograph whose 2025 measurements, combined with the first instrument's data, tighten and confirm the DMPP-7b parameters.","marker":"Pepe et al. 2013"},{"why":"Establishes the Dispersed Matter Planet Project and its selection of extremely low-activity stars, from which these three targets are drawn.","marker":"Haswell et al. 2020"},{"why":"Supplies the mass--radius relationship used to convert the confirmed and candidate masses into predicted radii for demographic placement.","marker":"M24"},{"why":"Defines the Neptunian desert, ridge, and savannah regions against which the paper locates DMPP-7b.","marker":"CG24"}],"fun_headline_variants":["DMPP-7b: a 0.72-Saturn-mass planet in a 4.93-day orbit","Bayesian analysis confirms DMPP-7b, finds two candidate super-Earths","Saturn-mass planet confirmed, two possible super-Earths flagged in DMPP","DMPP-7 hosts a confirmed giant; two other signals remain inconclusive"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The planetary reading of the 4.93-day signal assumes that any stellar activity mimicking it would leave a trace in the spectral-line shapes or be absorbed by the Gaussian process, and that the two spectrograph datasets can be combined with constant per-instrument offsets; if the star instead produces a clean 4.93-day activity signal with no line-shape change, or if the offsets drift between runs, the planetary identification weakens.","fun_headline_variants_meta":{"raw":{"variants":["DMPP-7b: a 0.72-Saturn-mass planet in a 4.93-day orbit","Bayesian analysis confirms DMPP-7b, finds two candidate super-Earths","Saturn-mass planet confirmed, two possible super-Earths flagged in DMPP","DMPP-7 hosts a confirmed giant; two other signals remain inconclusive"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000796,"raw_usage":{"total_tokens":3674,"prompt_tokens":1289,"completion_tokens":2385,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":905,"completion_tokens_details":{"reasoning_tokens":2286}},"tokens_in":905,"tokens_out":2385,"duration_ms":19507,"temperature":1.0,"reasoning_tokens":2286,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-16T00:24:30.855945+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Continue monitoring DMPP-7's radial velocities across several more stellar rotation cycles while measuring the S-index, line width, and line asymmetry: a dynamical 4.93-day planet must stay phase-coherent with constant amplitude and no matching line-shape variability, whereas a stellar origin should eventually show amplitude or phase drift, a period change, or the same period appearing in the line-shape indicators.","supporting_citations":[],"review_version":1}