{"id":"95cb40be-6295-435c-be54-d5362e1158c5","arxiv_id":"2508.10145","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"New Rossiter-McLaughlin measurements show WASP-35b and TOI-622b are aligned and K2-237b is on a polar orbit, with the latter two measured for the first time.","lead":"Astronomers used a new spectrograph, PLATOSpec, to measure how three planets' orbits tilt relative to their stars' spins. Two planets orbit in line with their stars, while a third, K2-237b, orbits nearly perpendicular, a rare polar configuration.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"K2-237b polar-orbit claim rests on sparsely sampled R-M curve with fixed CCF width and limb darkening; need to verify that systematic uncertainties are not underestimated.","rationale":"The reader already identified the fixed CCF width and limb-darkening coefficients as the weakest assumption. My pass confirms that these are load-bearing for the K2-237b polar-orbit claim specifically, because the R-M amplitude and shape depend directly on these inputs and the data set is sparse (~21 in-transit points over three nights). The reader's conditional verdict (CONDITIONAL) is appropriate: the concern is about reproducibility and systematic error quantification, not a demonstrated error in the measurement. I do not see evidence that the measurement is wrong, so I would not change the verdict to REJECT or ACCEPT. The paper should report the fixed values and ideally include a sensitivity test; this is addressable in revision.","tokens_in":19331,"tokens_out":1149,"duration_ms":12227,"concrete_test":"Re-run the K2-237b MCMC fit with sigma left as a free parameter (with a wide prior) and with the quadratic limb-darkening coefficients varied by +/-0.05 or replaced with values from a different model grid (e.g., PHOENIX). If lambda shifts by more than ~10 degrees or the posterior becomes bimodal, the quoted uncertainty is underestimated and the polar-orbit claim needs a systematic-error term; if lambda remains at 91 +/- 7, the claim is robust.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is K2-237b's polar orbit (lambda = 91 +/- 7 deg). The R-M amplitude is set by v sin i*, and the shape by the CCF width sigma and the limb-darkening coefficients. The paper states sigma was 'measured on the data and fixed' but never reports the value, and the fixed quadratic limb-darkening coefficients from ExoCTK/ATLAS9 are also not listed. This matters because K2-237 has only ~21 in-transit points over three nights, with the transit lasting about 4 hours. With sparse phase coverage and a small number of in-transit points, the R-M model can be degenerate with respect to sigma, limb darkening, and v sin i*: a broader CCF and weaker limb darkening can both reduce the R-M amplitude, potentially shifting the inferred lambda. The paper does not include a systematic-error analysis or a test of the sensitivity of lambda to these fixed parameters. If the fixed values deviate from the true stellar/instrumental values, the quoted 7-degree uncertainty could be underestimated, and the polar-orbit interpretation could weaken.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper presents Rossiter-McLaughlin (R-M) measurements for three transiting gas giants obtained with the newly commissioned PLATOSpec spectrograph on the ESO 1.52 m telescope. For WASP-35b the authors measure lambda = 1+18/-19 deg, consistent with a previous HARPS-N measurement, and use this as a validation of the instrument. They report the first spin-orbit measurements for TOI-622b (lambda = -4 +/- 12 deg, psi = 16.1+8.0/-9.7 deg) and K2-237b (lambda = 91 +/- 7 deg, psi = 90.5+6.8/-6.2 deg). The paper interprets TOI-622b as aligned, consistent with quiet disc migration, and K2-237b as nearly polar, arguing that this configuration favors disc-free migration rather than disc-driven migration, and that K2-237b adds support to the 'preponderance of perpendicular planets' trend.","tokens_in":19606,"tokens_out":9035,"duration_ms":106866,"significance":"If the K2-237b result holds, it is a valuable addition to the small sample of hot Jupiters on polar orbits and bears directly on migration mechanisms. TOI-622b is also a rare data point: a sub-Jovian planet with a measured spin-orbit angle around an F-type star above the Kraft break. The paper has clear strengths: the complete radial-velocity tables are given in the appendix, three independent MCMC runs with convergence diagnostics are reported, and the analysis uses a public R-M implementation (ARoMEpy). The WASP-35 comparison provides a useful end-to-end validation of PLATOSpec. The main weakness is that the headline polar-orbit claim for K2-237b rests on a single, statistically tight lambda posterior whose sensitivity to fixed model inputs is not quantified.","major_comments":[{"comment":"The R-M model fixes sigma, the quadratic limb-darkening coefficients, and Rp/Rs, but the adopted numerical values of sigma and the limb-darkening coefficients are not reported anywhere in the manuscript. K2-237b's headline lambda = 91 +/- 7 deg is based on only 21 in-transit points (Table 1), and the R-M anomaly shape and amplitude depend directly on these fixed quantities. The quoted uncertainty is therefore purely statistical; a systematic shift from an incorrect fixed value is not quantified. Please report the fixed values and show that lambda and psi are stable over a plausible range of sigma and limb-darkening coefficients, or add a systematic term to the quoted uncertainties. A check for activity/spot contamination would also strengthen the claim.","section":"§2.2, Table 3, Fig. 3"},{"comment":"The quoted true spin-orbit angle psi = 16.1+8.0/-9.7 deg for TOI-622b is derived after identifying the 0.2658 c/d TESS peak as the stellar rotation period. The identification was explicitly guided by the period predicted from v sin i* (3.77 d), and the same v sin i* is later used with this period to calculate psi. The peak has SNR=5.19 and shifts between sectors. Since psi is advertised in the abstract as a result, the paper should state this self-consistency explicitly and ideally test how psi changes if the rotation period is chosen independently or treated as uncertain.","section":"§4.1, Fig. 4"}],"minor_comments":[{"comment":"Affiliation 10: 'Univesity' should be 'University'.","section":"Affiliations"},{"comment":"The header 'No. Exp. Time' is ambiguous; it should be split into 'No. of frames' and 'Exposure time'.","section":"Table 1"},{"comment":"The statement 'no RV offsets between the nights were included in the fit' is ambiguous for the joint HARPS-N + PLATOSpec fit; please clarify whether an offset between the two instruments was included.","section":"§2.1"},{"comment":"The query returning '10 systems' from the NASA database should specify the query date and database version for reproducibility.","section":"§4.3"},{"comment":"The brown simulated aligned orbit is helpful, but the caption does not state which parameters are held fixed for this simulation; please specify.","section":"Fig. 3"}],"recommendation":"major_revision","confidential_remarks":"This is a solid first-look paper for PLATOSpec and the WASP-35 validation is convincing. The main concern is that the central K2-237b polar-orbit claim lacks a systematic-error analysis: the fixed sigma and limb-darkening values are not reported, and no sensitivity test is shown. If the revision includes those details, the result should be publishable in A&A."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Plainly, this is a good, careful R-M paper that delivers two first spin-orbit measurements and a clean instrument validation. K2-237b's polar orbit (lambda = 91 ± 7 deg) is visually clear in Fig. 3, and the aligned-orbit comparison is strongly disfavored. That result is new and likely to stand. TOI-622b's aligned orbit (-4 ± 12 deg) is also new and useful, and the WASP-35b re-observation with PLATOSpec matches HARPS-N well, which gives me confidence the instrument is doing what it should. The MCMC procedures are standard, the RVs are in the appendix, and the discussion is notably honest: the authors do not overclaim disc-free migration for K2-237, and they explicitly leave open alternative explanations like late infall or unresolved companions. Good credit for that.\n\nThe main soft spot is a reporting gap rather than a statistical one. The CCF width sigma and the quadratic limb-darkening coefficients are fixed in the model but never tabulated; you only read that sigma was measured and LD came from ExoCTK/ATLAS9. Given the sparse K2-237 phase coverage (about 21 in-transit points over three nights, with a 4-hour transit), the model's sensitivity to those fixed values matters. A systematic-error test or even just table entries would address the main legitimate concern. The TOI-622 rotation period identification also rests on an SNR=5.19 peak; the peak is consistent across TESS sectors, so it is probably fine, but the psi derivation is mildly circular because v sin i* was used to pick the period. Minor, but worth a sentence. The instrument description relying on an in-prep paper is normal for a new facility.\n\nThese are all revision-level items. The central lambda measurements are not undermined. For the field, this paper adds a polar hot Jupiter to a small club and extends the sparse sub-Jovian sample above the Kraft break. Anyone working on obliquity demographics or migration mechanisms will want to cite it.\n\nMy recommendation: send to a serious referee. The reporting gaps are fixable, the data quality looks adequate for the claims, and the polar result is significant enough to warrant careful external checks. I would accept after those additions.","headline":"A solid R-M measurement paper: the K2-237b polar orbit looks real, and the main fixable weakness is missing reporting of fixed model parameters.","tokens_in":20146,"tokens_out":1633,"would_cite":true,"duration_ms":21369,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["97.82.Fs","96.60.Bn"],"model":"deepseek-v4-flash","headline":"A hot Jupiter orbits its star nearly perpendicular to the stellar spin, a polar configuration pointing to disc-free migration.","keywords":["spin-orbit misalignment","Rossiter-McLaughlin effect","hot Jupiter","polar orbit","exoplanet migration","PLATOSpec","K2-237b","TOI-622b"],"falsifier":"Re-measure K2-237b's Rossiter–McLaughlin effect with a different spectrograph (e.g., ESPRESSO at the VLT) or with an independent modeling code that either fits the CCF shape directly or marginalizes over limb-darkening parameters, and check whether $\\lambda$ remains consistent with 90 degrees rather than, say, 60 or 120 degrees.","tokens_in":19240,"feed_emoji":"🪐","tokens_out":3698,"duration_ms":30844,"temperature":0.7,"pith_summary":"The paper uses a newly commissioned ground-based spectrograph, PLATOSpec, to measure the Rossiter–McLaughlin effect — the subtle shift in starlight during a planet's transit — for three giant planets. For K2-237b, the key discovery, it finds the planet's orbit is very nearly perpendicular to its host star's spin axis, with projected spin-orbit angle $\\lambda = 91 \\pm 7$ degrees and true angle $\\psi = 90.5^{+6.8}_{-6.2}$ degrees. The other two planets, WASP-35b and TOI-622b, show well-aligned orbits. A polar orbit is hard to produce by the usual disc-migration picture, so the paper argues K2-237b likely migrated through a disc-free, high-eccentricity pathway, and uses tidal timescale arguments to show the misalignment is primordial. A careful reader would care because spin-orbit angles are one of few observable fossil records of how giant planets form and migrate.","feed_headline":"Hot Jupiter K2-237b orbits its star pole-on","feed_subtitle":"New spin-orbit measurements reveal a near-perpendicular orbit, pointing to disc-free migration.","key_machinery":"The Rossiter–McLaughlin (R-M) effect: during a transit, the planet occulting part of the rotating stellar disk creates an asymmetric spectral-line profile, which appears as an anomalous Doppler shift that depends on the sky-projected angle $\\lambda$ between the stellar spin axis and the orbital normal. The analysis fits a Keplerian plus R-M model (via the ARoMEpy implementation) to high-resolution PLATOSpec RVs, then converts $\\lambda$ to the true 3D spin-orbit angle $\\psi$ using the stellar inclination from the rotation period and $v \\sin i_*$.","core_discovery":"For six transits of three gas giants observed with PLATOSpec at La Silla, the paper measures the projected spin-orbit angle from the Rossiter–McLaughlin anomaly. It finds WASP-35b aligned ($\\lambda = 1^{+19}_{-18}$ deg, agreeing with the HARPS-N value of $-5 \\pm 11$ deg), TOI-622b aligned ($\\lambda = -4 \\pm 12$ deg), and — for the first time — K2-237b on a nearly perfect polar orbit ($\\lambda = 91 \\pm 7$ deg, $\\psi = 90.5^{+6.8}_{-6.2}$ deg). Since the host star sits around the Kraft break with a radiative envelope, tidal realignment is extremely slow ($\\tau_{\\rm RA} \\approx 10^{15}$ yr), so the polar orbit cannot be a later tidal product. The paper interprets this as evidence that K2-237b's","pith_inferences":["The polar orbit of K2-237b, if real, is a strong constraint on disc-driven migration models: standard Type II or disc-warping mechanisms produce misalignments up to tens of degrees but rarely a configuration so close to 90 degrees, so the paper's disc-free interpretation is likely the simplest reading.","A testable extension: measure the sky-projected angle of K2-237b at multiple epochs or search for transit-timing variations with higher precision — a primordial polar orbit should be stable over years, while a Kozai–Lidov-driven orbit would show long-term precession or additional companions.","The paper's claim that TOI-622b is aligned despite an F-type host above the Kraft break is a single-object counterexample to the trend proposed for more massive stars; if more sub-Jovian planets around F stars are found aligned, it would weaken that proposed trend.","The fixed limb-darkening coefficients and single CCF-width assumption are the most fragile part of the measurement; an independent check with different limb-darkening laws or a full R-M model that fits the CCF shape directly would confirm the polar result."],"forward_implications":["K2-237b joins a small set of planets in polar orbits, and its configuration strengthens the statistical evidence that some orbital architectures — especially near-perpendicular alignments — are preferred over others.","TOI-622b adds a rare data point for sub-Jovian planets around stars above the Kraft break, a parameter space where tidal realignment is inefficient, helping test whether hot stars' sub-Jovian planets are preferentially misaligned.","If K2-237b's polar orbit is primordial, then its migration occurred via disc-free high-eccentricity mechanisms, and future atmospheric C/O measurements could test this by looking for accretion signatures.","PLATOSpec on a 1.5-m telescope delivers R-M measurements consistent with HARPS-N on a 3.6-m telescope for WASP-35b, demonstrating that modest-aperture, high-resolution spectrographs can supply the ground-based follow-up needed by PLATO and Ariel.","The true 3D angle $\\psi$ for K2-237b is consistent with a polar orientation, but the projected angle $\\lambda = 91$ deg already rules out an aligned orbit at high significance."],"supporting_citations":[{"why":"Provides the HARPS-N spin-orbit measurement of WASP-35b used as the comparison and joint-fit dataset that validates PLATOSpec's performance.","marker":"[Zak et al. (2025a)]"},{"why":"Discovery and characterization paper for K2-237, including the rotation period used to derive the stellar inclination and true angle $\\psi$.","marker":"[Soto et al. (2018)]"},{"why":"Discovery and characterization of TOI-622, supplying the ephemeris, radius, mass, and age priors used in the fit and interpretation.","marker":"[Psaridi et al. (2023)]"},{"why":"Supplies the tidal realignment timescale formulas for convective and radiative envelopes used to argue K2-237b's polar orbit is primordial.","marker":"[Albrecht et al. (2012)]"},{"why":"Previous methodology paper establishing the R-M fitting approach that this work follows.","marker":"[Zak et al. (2024b)]"},{"why":"Provides the statistical method used to derive the true spin-orbit angle $\\psi$ from $v \\sin i_*$ and the rotation period.","marker":"[Masuda & Winn (2020)]"},{"why":"Supplies independent transit characterization data for K2-237 used in the literature priors.","marker":"[Smith et al. (2019)]"},{"why":"Earlier study reporting transit-timing variations and orbital decay for K2-237, whose disc-migration interpretation the paper's polar orbit contradicts.","marker":"[Yang et al. (2024)]"}],"fun_headline_variants":["K2-237b orbits its star pole-on","New spin-orbit data show K2-237b on polar orbit","K2-237b's polar orbit points to disc-free migration","PLATOSpec finds K2-237b orbiting pole-on","First polar orbit measurement for hot Jupiter K2-237b"],"cache_read_input_tokens":2816,"weakest_assumption_plain":"The Rossiter–McLaughlin model, with fixed quadratic limb-darkening coefficients from stellar-atmosphere models and a single measured CCF width, correctly represents the transit-time velocity shifts for K2-237b.","fun_headline_variants_meta":{"raw":{"variants":["K2-237b orbits its star pole-on","New spin-orbit data show K2-237b on polar orbit","K2-237b's polar orbit points to disc-free migration","PLATOSpec finds K2-237b orbiting pole-on","First polar orbit measurement for hot Jupiter K2-237b"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000263,"raw_usage":{"total_tokens":1538,"prompt_tokens":945,"completion_tokens":593,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":689,"completion_tokens_details":{"reasoning_tokens":505}},"tokens_in":689,"tokens_out":593,"duration_ms":6309,"temperature":1.0,"reasoning_tokens":505,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-05T20:38:09.867052+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Re-measure K2-237b's Rossiter–McLaughlin effect with a different spectrograph (e.g., ESPRESSO at the VLT) or with an independent modeling code that either fits the CCF shape directly or marginalizes over limb-darkening parameters, and check whether $\\lambda$ remains consistent with 90 degrees rather than, say, 60 or 120 degrees.","supporting_citations":[{"cited_title":"G., Díaz, M","cited_arxiv_id":null,"evidence_quote":"Discovery and characterization paper for K2-237, including the rotation period used to derive the stellar inclination and true angle $\\psi$."},{"cited_title":"2023, A&A, 675, A39","cited_arxiv_id":null,"evidence_quote":"Discovery and characterization of TOI-622, supplying the ephemeris, radius, mass, and age priors used in the fit and interpretation."},{"cited_title":"N., Johnson, J","cited_arxiv_id":null,"evidence_quote":"Supplies the tidal realignment timescale formulas for convective and radiative envelopes used to argue K2-237b's polar orbit is primordial."},{"cited_title":"& Winn, J","cited_arxiv_id":null,"evidence_quote":"Provides the statistical method used to derive the true spin-orbit angle $\\psi$ from $v \\sin i_*$ and the rotation period."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies independent transit characterization data for K2-237 used in the literature priors."},{"cited_title":"J., Kerins, E., et al","cited_arxiv_id":null,"evidence_quote":"Earlier study reporting transit-timing variations and orbital decay for K2-237, whose disc-migration interpretation the paper's polar orbit contradicts."}],"review_version":1}