Dynamical Mass Constraints on Transition Disk Perturbers with the G23H Catalog

We present dynamical mass constraints on perturbers in 11 transition disk systems using a novel combination of calibrated Hipparcos and Gaia absolute astrometry data. Out of the sample of 11, we find support for companions in seven systems, with significant detections in three. These systems are: HD 142527, where we clearly detect the known low-mass stellar companion HD 142527 B; AB Aurigae, where we detect a low-mass stellar or sub-stellar companion; and MWC 758, where we detect a likely sub-stellar companion. We also find strong evidence of companions to HD 97048 and UX Tau A, and moderate evidence for companions to HD 100546 and CQ Tau. In the four systems with non-detections, we find no evidence for companions more massive than $\sim$6 $M_{\mathrm{Jup}}$ with a semi-major axis greater than 3 au for HD 100453, nor for companions more massive than $\sim$2 $M_{\mathrm{Jup}}$ with a semi-major axis greater than 2 au for TW Hya. We also find no evidence for stellar mass companions with semi-major axes between $\sim$3 and $\sim$25 au for both HD 34282 and RY Lup. In addition to our fiducial model, we perform cross validation between astrometry sources. By comparing results across models, we find tentative evidence of a short timescale excess astrometric noise that may impact some protoplanetary disk systems. We conclude with predictions for the prospects of making dynamical mass constraints on protoplanets in protoplanetary disk systems with Gaia data release 4 using detailed simulations of Gaia DR4 data of PDS 70 and WISPIT 2.

💡 Research Summary

This paper presents a systematic dynamical‑mass analysis of potential companions in eleven transition‑disk systems by exploiting a newly calibrated astrometric dataset, the G23H catalog, which merges Hipparcos, Gaia DR2, and Gaia DR3 measurements into a common reference frame and applies bias‑corrected excess‑noise estimates (UEV A). The authors argue that earlier Gaia‑only studies suffered from uncorrected reference‑frame rotations, underestimated uncertainties, and systematic biases that limit sensitivity to sub‑stellar companions. By using the calibrated proper motions, long‑baseline position differences (GDR32), and the UEV A correction, they achieve a more reliable astrometric signal for each target.

The sample consists of eleven stars that are both Hipparcos entries and known transition‑disk hosts (AB Aur, CQ Tau, HD 34282, HD 97048, HD 100453, HD 100546, HD 142527, MWC 758, RY Lup, TW Hya, UX Tau A). For each system the authors run four Bayesian orbital models with the Octofitter 10 code: (i) a “jitter” model that includes all calibrated proper‑motion measurements plus a free jitter term for Gaia excess noise; (ii) a co‑planar jitter model that adds a Gaussian prior (σ = 10°) on the mutual inclination between the companion orbit and the disk plane; (iii) a “no‑jitter” model that omits the jitter term and the co‑planarity prior; and (iv) a UEV A model that directly incorporates the unbiased excess‑noise estimator. Sampling is performed with non‑reversible parallel tempering (12 rounds, 4096 posterior samples). Priors on semi‑major axis, companion mass, and orbital angles are broad and largely uninformative, allowing the data to dominate the inference.

Model comparison is performed via Bayes factors (BF), interpreted as odds ratios under equal prior model probabilities. The authors adopt BF > 3 as “evidence for a companion” and BF > 20 as “statistically significant detection.” The results are striking: three systems show highly significant astrometric signatures—HD 142527 (re‑detecting the known low‑mass stellar companion HD 142527 B), AB Aur (new low‑mass stellar or massive sub‑stellar companion), and MWC 758 (likely sub‑stellar companion). Four additional systems exhibit moderate evidence (BF ≈ 10–3): HD 97048 and UX Tau A (strong evidence), HD 100546 and CQ Tau (moderate evidence). The remaining four (RY Lup, HD 100453, HD 34282, TW Hya) show no evidence (BF < 1); the authors place upper limits of ≈2 M_Jup (for semi‑major axes > 2 au) to ≈6 M_Jup (for > 3 au) on any unseen companions.

Comparing the four models reveals that the inclusion of the UEV A term can alter the inferred significance in some cases, suggesting that short‑timescale excess noise—potentially arising from bright, asymmetric disk structures—may masquerade as a companion signal. The co‑planar jitter model yields slightly tighter mass–semi‑major‑axis posteriors, reflecting the physical expectation that protoplanets should orbit near the disk plane.

Beyond the current dataset, the authors simulate Gaia Data Release 4 (DR4) observations for two well‑studied protoplanet hosts, PDS 70 and WISPIT 2. Using GDR3‑based noise estimates corrected by UEV A, they generate synthetic astrometric time series up to March 2026. The simulations indicate that DR4 will be capable of detecting companions down to ≲1 M_Jup at separations of a few astronomical units—an improvement of one to two orders of magnitude over the present G23H constraints. This suggests that the forthcoming Gaia release will open a new window on the demographics of planets embedded in protoplanetary disks.

In summary, the paper (1) establishes a robust, calibrated astrometric framework for probing low‑mass companions in transition‑disk systems, (2) provides concrete dynamical mass and orbital‑radius limits for eleven targets, including three new significant detections, and (3) forecasts the transformative potential of Gaia DR4 for direct dynamical mass measurements of protoplanets. The work underscores the importance of careful bias correction and multi‑epoch cross‑validation when pushing astrometric techniques into the planetary‑mass regime, and it sets the stage for large‑scale, astrometry‑based surveys of planet formation environments in the near future.