{"id":"1162702c-0d4f-4fa8-8413-c8b5541efd27","arxiv_id":"2412.06404","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":8,"one_line_summary":"A joint fit of radial velocities and astrometric acceleration detects an 8.4 Jupiter-mass planet on a 5.7 au, eccentric orbit around HD 57625.","lead":"Astronomers report a giant planet, HD 57625 b, around a nearby star, detected by combining a direct imaging non-detection, 13 years of stellar wobble measurements, and astrometric acceleration from Hipparcos and Gaia. The result adds a rare true-mass giant planet on a wide, eccentric orbit and shows how multiple techniques can find planets that any one method alone would miss.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Single-companion attribution of the PMa is the load-bearing step that yields the true mass; without an alternative-model test the 8.4 MJup value is conditional.","rationale":"The reader's weakest_assumption identifies the same load-bearing risk. My independent reading confirms it is the main issue: the RV-only fit is phase-incomplete, with a period close to the observational baseline and a loosely constrained K, while the PMa is only a two-epoch proper-motion difference. The conversion from minimum mass to true mass therefore hinges entirely on the assumption that one companion produces both signals. The paper's internal checks, such as activity-index correlations, exclusion of the wide stellar companion, and detection-completeness maps, reduce but do not eliminate this risk: a second companion below the current detection thresholds, or a systematic in the cross-calibrated PMa, would shift the fitted inclination and true mass. No internal inconsistency was found; the analysis is plausible and well documented, but the single-companion premise should be tested explicitly before the true-mass claim is taken as final. A concrete model comparison with a second Keplerian or an extra acceleration term, plus an alternate PMa catalog, would settle the question.","tokens_in":20955,"tokens_out":6878,"duration_ms":82316,"concrete_test":"Refit RV+PMa with orvara/PyORBIT adding (a) a second circular Keplerian at the 1300 d residual period and (b) a free linear acceleration term to absorb an unseen outer companion; compare delta-BIC and posterior mass shift against the one-planet model. Also repeat the fit using Brandt (2021) HGCA PMa instead of Kervella et al. (2022) values. If the 8.43 MJup posterior shifts by more than its 1-sigma error or delta-BIC favors the two-signal model, the single-companion interpretation is not secure.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Load-bearing concern: the joint orvara fit of Sect. 5 and Table 4 attributes the entire Hipparcos-Gaia proper-motion anomaly to exactly the one Keplerian seen in the SOPHIE RVs. That single attribution is what upgrades the RV minimum mass (5.79 MJup, Table 3) to a true mass (8.43 MJup) and to an inclination (43.8 deg). It is not directly tested. The astrometric constraint is only the difference between two catalog proper-motion epochs (Fig. 6), not a resolved orbit, so it cannot by itself distinguish one companion from two or from catalog systematics. The RV baseline (4708 d) is shorter than the fitted period (~4843 d), and the RV-only K upper uncertainty is ~25% (Sect. 4), so the RV data are also weak guards against an additional long-period or 1300 d signal (the residual peak has FAP = 6%). A second companion contributing to the PMa, or a cross-calibration systematic in the Kervella/HGCA acceleration, would bias the fitted inclination and true mass. The paper presents no two-companion or extra-acceleration alternative model, so this key premise is assumed rather than demonstrated.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports the first result of an ongoing SHARK-NIR high-contrast imaging survey of stars with significant proper-motion anomalies. For the F8 star HD 57625, the authors combine SHARK-NIR H-band and LBTI/LMIRCam L'-band imaging non-detections with archival SOPHIE radial velocities and the Hipparcos-Gaia proper-motion anomaly, modeled jointly with the orvara MCMC code. They report the detection of HD 57625 b, a giant planet with true mass 8.43(+1.10,-0.91) M_Jup, semi-major axis 5.70(+0.14,-0.13) au, and eccentricity 0.52(+0.04,-0.03). The imaging non-detection is used to exclude stellar and massive brown-dwarf companions, and a multi-technique injection-recovery completeness analysis is presented. The paper explicitly acknowledges the limited RV phase coverage and the resulting uncertainties in the RV-only orbital solution.","tokens_in":21269,"tokens_out":5326,"duration_ms":56281,"significance":"If the inferred parameters are correct, HD 57625 b is a useful addition to the small sample of wide-orbit giant planets with true masses determined by combining radial velocities and astrometry, and it demonstrates the scientific return of the SHARK-NIR survey. The paper's strengths are its explicit use of public datasets (SOPHIE, Hipparcos, Gaia), its quantitative MCMC treatment with orvara, and its injection-recovery completeness maps that combine imaging, RV, and astrometric data. The main weakness is that the true-mass and inclination claims rest on the untested assumption that the full proper-motion anomaly is produced by the single Keplerian companion detected in the RVs; the paper does not present a two-companion or extra-acceleration alternative model.","major_comments":[{"comment":"The conversion of the RV-only minimum mass (5.79 M_Jup, Table 3) into the true mass (8.43 M_Jup) and inclination (43.8 deg) is entirely driven by the assumption in the joint orvara fit that the Hipparcos-Gaia proper-motion anomaly is produced by the same single Keplerian companion seen in the SOPHIE RVs. This assumption is not tested. The astrometric constraint is only an epoch-difference proper motion (Fig. 6), not a resolved orbit, so it cannot by itself distinguish one companion from two or from catalog systematics. Given that the RV baseline (4708 d) is shorter than the fitted period (~4843 d), that the RV-only K upper uncertainty is about 25%, and that the residual periodogram shows a 1300 d peak at 6% FAP (Section 4), a second companion or an additional acceleration contributing to the PMa is not excluded. Please add an explicit two-companion or extra-acceleration model comparison, or at least a quantitative bound on a possible second contribution, and state how the quoted M_b and i_b would change under such a model.","section":"Section 5, Table 4"},{"comment":"The astrometric input used in the joint fit is not stated precisely enough. The paper initially quotes the Kervella et al. (2022) PMa with SNR 11.04 and uses that catalog for the sensitivity curve in Fig. 5, but it then says that orvara is designed to use the PMa from the Hipparcos-Gaia Catalog of Accelerations (HGCA, Brandt 2018, 2021). These catalogs have different cross-calibration treatments, and the adopted PMa values, uncertainties, and covariances directly affect the fitted inclination and true mass. Please state explicitly which PMa dataset was input to orvara and confirm that the Table 4 results are unchanged when the other catalog is used.","section":"Section 5 and Table 1"},{"comment":"The RV-only posterior for the orbital period may be weakly constrained by the prior choice U(2000, 10000) d because the baseline is only 4708 d, close to the fitted period. The paper acknowledges the incomplete phase coverage, but it should also show that the quoted period uncertainty is not prior-dominated, for example by reporting the prior and posterior probability density functions for P_b or by testing a wider period prior. This is important because the joint solution's period and semi-major axis inherit the RV period information.","section":"Section 4, Table 3"}],"minor_comments":[{"comment":"The caption labels the green circles as the reference epochs for Hipparcos and Gaia DR3 (1991 and 2024), but the Gaia DR3 reference epoch is approximately 2016, while 2024 is the epoch of the imaging observation. Please correct this labeling.","section":"Figure 7 caption"},{"comment":"The prior line for inclination reads 'cos i, U(0, 180)', which is ambiguous. Please clarify whether the prior is uniform in cos i over [-1, 1] or uniform in i over [0, 180] degrees.","section":"Table 4"},{"comment":"In the discussion of the distant stellar companion, the statement that a 0.2 M_sun companion would produce the reported acceleration only at ~70 au appears to assume a circular orbit; please state this assumption explicitly.","section":"Section 5"},{"comment":"The residual periodogram peak at ~1300 d with FAP = 6% is described as non-significant, but given the paper's reliance on a single-Keplerian model, a sentence explaining why this peak cannot be due to a second companion would be helpful.","section":"Section 4"}],"recommendation":"major_revision","confidential_remarks":"The paper is well suited to A&A and the multi-technique dataset is appropriate. The main issue is the untested single-companion attribution of the PMa, which is load-bearing for the true-mass claim. If the authors can demonstrate with an alternative-model test that a second companion or an extra acceleration does not change the inferred mass and inclination by more than the quoted uncertainties, I would be willing to support acceptance."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Short version: this is a real object-level detection—HD 57625 b—from public SOPHIE RVs plus the Hipparcos-Gaia PMa, with a non-detection in new SHARK-NIR/LMIRCam imaging. The RV-only solution is honest about its incomplete phase coverage, and the joint fit gives a plausible 8.4 MJup true mass. The main caveat: that true mass and inclination depend on attributing the entire PMa to the same single Keplerian seen in the RVs. The assumption is not directly tested.\n\nWhat the paper does well: it uses archival data transparently, reports the RV-only limitations clearly (period comparable to the 4708 d baseline, K upper uncertainty ~25%), and uses the imaging non-detection correctly to exclude stellar companions and massive brown dwarfs rather than claim a detection. The detection completeness maps are a nice addition, showing where each technique is blind and how they complement each other. The writing is clear and the literature is cited appropriately, including the earlier PMa hint and the RV trend.\n\nWhere it gets soft: the orvara joint fit is the load-bearing step. The PMa is a two-epoch proper-motion difference, so it cannot by itself distinguish one companion from two or from cross-calibration systematics. The RV residual peak at ~1300 d has FAP = 6%, and the orbital period is longer than the RV baseline; a second companion contributing to the PMa would bias the inclination and true mass. The paper does not present a two-companion or extra-acceleration alternative model. That is a real gap, but it is a gap in robustness rather than evidence the planet isn't there. The RV-only minimum mass (5.8 MJup) and the PMa-compatible mass range overlap, so the detection itself is on solid ground; the 'true mass' is conditional on the single-companion hypothesis.\n\nWho gets value: anyone working on wide-orbit giant planet demography, true mass measurements, or multi-technique survey strategy. The paper is competent and the result is useful even with the caveat. I would send it to a serious referee; the limitations can be addressed in revision by testing at least a two-companion model and reporting the orvara/PyORBIT configurations. The authors have done a fair job of presenting the evidence.","headline":"A genuine multi-technique detection of a wide-orbit giant planet, whose true mass is conditional on a single-companion attribution of the proper-motion anomaly.","tokens_in":22027,"tokens_out":3008,"would_cite":true,"duration_ms":29126,"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":"Archival radial velocities and Hipparcos-Gaia proper motion data jointly reveal a giant planet, HD 57625 b, with a true mass of 8.4 Jupiter masses on a 5.7 AU eccentric orbit.","keywords":["exoplanets","radial velocity","astrometry","proper motion anomaly","direct imaging","giant planets","eccentric orbits","HD 57625"],"falsifier":"Measure one full radial-velocity orbit (the fitted period is roughly 4,850 days while the available data span 4,708 days) and obtain an independent astrometric orbit from future Gaia data. The single-Keplerian model predicts a specific position-angle track on the sky and a 43.8-degree inclination; if the new data require a different period, a second companion, or a different inclination, the claimed true mass of 8.4 Jupiter masses is wrong.","tokens_in":20787,"feed_emoji":"🪐","tokens_out":7907,"duration_ms":75458,"temperature":0.7,"pith_summary":"HD 57625, an F8 star 44 parsecs away, has been hiding a giant planet that neither radial velocities nor astrometry could identify on their own. By combining 13 years of archival radial-velocity measurements with the discrepancy between Hipparcos and Gaia proper motions, the paper detects HD 57625 b: a planet of about 8.4 Jupiter masses on a 5.7 au orbit with eccentricity 0.52. The astrometric signal breaks the usual inclination degeneracy, so the mass is a true dynamical mass rather than a minimum mass. A high-contrast imaging campaign detected nothing, which independently rules out stellar and brown-dwarf companions at the relevant separations. This matters because true-mass outer giant planets are rare and are needed to test how such systems form and evolve.","feed_headline":"Wobble data reveal an eccentric giant planet, 8.4 Jupiter masses","feed_subtitle":"Archival radial velocities plus Hipparcos-Gaia astrometry pin a true mass on a 5.7-AU orbit.","key_machinery":"The proper motion anomaly (PMa) - the statistically significant difference between a star's long-term proper motion, measured by comparing Hipparcos and Gaia, and its short-term proper motion - is the astrometric signal that reveals the star is accelerating. The paper's central mechanism is a joint Markov-chain Monte Carlo fit that models the radial velocities and the PMa with the same single Keplerian orbit, producing orbital elements and a true mass rather than a minimum mass. The imaging contrast curves contribute a second, independent constraint by showing that no stellar or high-mass brown-dwarf companion could have escaped detection, leaving only the substellar-mass interpretation.","core_discovery":"The paper's central claim is that the accelerating star HD 57625 hosts a genuine planetary-mass companion, HD 57625 b, with a dynamical mass of $8.43^{+1.10}_{-0.91}$ $M_{\\rm Jup}$, a semimajor axis of $5.70^{+0.14}_{-0.13}$ au, and an eccentricity of $0.52^{+0.04}_{-0.03}$. The companion is responsible for both the long-term Keplerian trend visible in the archival radial velocities and the significant proper motion anomaly between Hipparcos and Gaia. Jointly fitting the two datasets yields an orbital inclination of $43.8^{+14.3}_{-7.2}$ degrees, which converts the radial-velocity minimum mass into a true mass and places the object firmly below the roughly 13 $M_{\\rm Jup}$ deuterium-burning limit. The imaging non-detection sets contrast limits that exclude stellar and massive brown-dwarf companions, so the substellar interpretation is confirmed by three independent datasets.","pith_inferences":["If the same joint RV-plus-PMa analysis is applied to other accelerating stars with archival RV trends, the sample of outer giant planets with true masses could grow substantially without waiting for full-orbit RV coverage.","The published relative astrometric orbit predicts where HD 57625 b should appear on the sky; an imaging observation with a smaller inner working angle, timed near the predicted position, could test the orbital solution directly.","The moderately eccentric orbit and the presence of a wide stellar companion suggest that similar systems with PMa-detected giants may preferentially show Kozai-excited eccentricities; this is a testable prediction for the survey sample."],"forward_implications":["HD 57625 b becomes one of the few dozen outer giant planets with a true dynamical mass, so population studies can use it without the sin i degeneracy.","Because the imaging observations rule out stellar and brown-dwarf companions at separations beyond about 5 au, the planetary interpretation of the RV and PMa signals is independently supported.","The multi-technique completeness maps show that additional inner low-mass planets and wide-orbit giant planets could still be present, defining the discovery space for future observations.","The estimated Kozai timescale, between about 2 and 39 million years, is much shorter than the star's 4.8-billion-year age, so the distant stellar companion is a plausible driver of the planet's high eccentricity if the mutual inclination exceeds about 39 degrees."],"supporting_citations":[{"why":"Supplies the proper motion anomaly measurement with signal-to-noise 11.04 that selected the target and anchors the astrometric constraint on companion mass.","marker":"Kervella et al. (2022)"},{"why":"Provides the joint-fitting method used to combine radial velocities and proper motion anomaly into the Keplerian solution with true mass and inclination.","marker":"Brandt et al. (2021)"},{"why":"Establishes the cross-calibrated Hipparcos-Gaia acceleration catalog that defines the proper motion anomaly used in the fit.","marker":"Brandt (2018, 2021)"},{"why":"Supplies Gaia DR3 astrometry, distance, and stellar parameters used for the host-star characterization and PMa reference.","marker":"Gaia Collaboration et al. (2023)"},{"why":"Provides the Hipparcos catalog proper motions needed to compute the long-term proper motion and the PMa.","marker":"van Leeuwen (2007)"},{"why":"Documents the SOPHIE fibre upgrade, justifying the split of the RV data into two independent zero-point datasets.","marker":"Bouchy et al. (2013)"},{"why":"Describes the SOPHIE spectrograph whose public archive supplies the 70 radial-velocity measurements.","marker":"Perruchot et al. (2008)"},{"why":"Provides the AMES-COND atmospheric models used to convert imaging contrast limits into companion mass limits.","marker":"Allard et al. (2003)"}],"fun_headline_variants":["Astrometry and RV nail an eccentric giant planet's true mass","HD 57625 b: 8.4-Jupiter-mass planet on a wide eccentric orbit","Combined RV and astrometry pin an eccentric planet at 5.7 AU","Eccentric giant planet HD 57625 b weighed at 8.4 Jupiter masses"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The detection assumes that the measured wobble in the star's radial velocity and the change in its motion across the sky are produced by one and the same unseen planet, and not by a second companion or by systematic errors in the merged star catalogs.","fun_headline_variants_meta":{"raw":{"variants":["Astrometry and RV nail an eccentric giant planet's true mass","HD 57625 b: 8.4-Jupiter-mass planet on a wide eccentric orbit","Combined RV and astrometry pin an eccentric planet at 5.7 AU","Eccentric giant planet HD 57625 b weighed at 8.4 Jupiter masses"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.00191,"raw_usage":{"total_tokens":7583,"prompt_tokens":1148,"completion_tokens":6435,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":764,"completion_tokens_details":{"reasoning_tokens":6346}},"tokens_in":764,"tokens_out":6435,"duration_ms":39929,"temperature":1.0,"reasoning_tokens":6346,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T19:42:21.671516+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure one full radial-velocity orbit (the fitted period is roughly 4,850 days while the available data span 4,708 days) and obtain an independent astrometric orbit from future Gaia data. The single-Keplerian model predicts a specific position-angle track on the sky and a 43.8-degree inclination; if the new data require a different period, a second companion, or a different inclination, the claimed true mass of 8.4 Jupiter masses is wrong.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes the cross-calibrated Hipparcos-Gaia acceleration catalog that defines the proper motion anomaly used in the fit."},{"cited_title":"F., Hébrard, G., et al","cited_arxiv_id":null,"evidence_quote":"Documents the SOPHIE fibre upgrade, justifying the split of the RV data into two independent zero-point datasets."},{"cited_title":"2008, in Society of Photo-Optical In- strumentation Engineers (SPIE) Conference Series, V ol","cited_arxiv_id":null,"evidence_quote":"Describes the SOPHIE spectrograph whose public archive supplies the 70 radial-velocity measurements."},{"cited_title":"2003, in IAU Symposium, V ol","cited_arxiv_id":null,"evidence_quote":"Provides the AMES-COND atmospheric models used to convert imaging contrast limits into companion mass limits."}],"review_version":1}