Detecting and Characterizing Companions with a Calibrated Gaia DR2, DR3, and Hipparcos Catalog (G23H)

TL;DR

We address the challenge of detecting and characterizing companions via astrometry by constructing a calibrated, Gaia DR3-referenced catalog that fuses Hipparcos, Gaia DR2/DR3, HGCA, and Gaia noise/RV metrics. A joint likelihood implemented in Octofitter forward-models Gaia measurement epochs, UEVA, proper motions, Hipparcos IAD, and Gaia RV variability to derive full orbital posteriors for potential companions, marginalizing over calibration uncertainties. The method recovers most known exoplanetary and binary systems within 40 pc, provides independent confirmation of planets (e.g., 14 Her b) using Gaia/Hipparcos data alone, and exposes a low false-positive rate among RV-quiet stars. The authors release a public catalog and an updated Octofitter (v8), enabling the community to integrate these constraints into multi-technique exoplanet studies and to exploit Gaia DR4 epoch data once available.

Abstract

Gaia DR4 epoch astrometry will enable the detection of thousands of exoplanets through astrometric motion. Here, we present a composite catalog and modeling framework that extracts the maximum information from existing Hipparcos and Gaia data releases. We calibrate Gaia DR2 proper motions and DR3-DR2 scaled position differences against the Gaia DR3 reference frame, and combine these with the Hipparcos-Gaia Catalog of Accelerations, the Hipparcos intermediate astrometric data, Gaia astrometric excess noise, and Gaia radial velocity variability constraints. We implement a joint likelihood model for these data in Octofitter that marginalizes over Gaia's unpublished observation epochs. This results in full orbit posteriors that can be computed uniformly for a large class of companions. We compare these posteriors to published orbital solutions for 25 stellar binaries from the Sixth Catalog of Orbits of Visual Binary Stars, recovering all companions at high significance and broadly consistent orbital separations. We then recover independent evidence to support 94 of 120 tested Jovian exoplanetary systems from the NASA Exoplanet Archive (plus 3 known stellar companions, and one previously detected planet we now rule out). We demonstrate that in cases like 14 Her b, the posteriors confirm the planetary nature of a signal using only Gaia and Hipparcos data. We find no false positives among 25 RV-quiet standard stars without significant Hipparcos-Gaia accelerations. Our method can break degeneracies inherent to proper motion anomaly or excess noise modeling alone by resolving orbital curvature within the Gaia baseline. The catalog and updated Octofitter are made publicly available to the community.

Figures (23)

• Figure 1: Conceptual schematic (not to scale) showing how the different datasets correspond to different time ranges. Linear sky motion is shown without the addition of annual parallax. The proper motions for each data source result from published linear fits to the perturbed motion over different time windows kervella_stellar_2019hgca_dr2. The UEVA Gaia astrometric excess noise constraint is deduced from published uncertainty inflation applied within the GDR3 linear fit pmex1. The RV variability is deduced from the uncertainty in the published mean Gaia RV of the star, itself calculated from the sample variance over the GDR3 baseline paired The two scaled position differences $\mathbf{\mu_{\rm HG}}$ and $\mathbf{\mu_{\rm DR32}}$ are calculated from the displacement over the time difference between the Hipparcos and GDR3 positions (sourced from the HGCA), and GDR2 and GDR3 positions respectively. The IAD is the only source where each individual measurement is available for modeling. The net proper motion and positions of the IAD are marginalized out to avoid double-counting with the HGCA.
• Figure 2: Correction applied to the GDR2 proper motions and uncertainties (Section \ref{['sec:cal-dr2-dr3']}). The colors indicate the median correction within each Healpix level 6 bin.
• Figure 3: Z-scores of corrected GDR2 proper motions compared to GDR3.
• Figure 4: Correction applied to the GDR3--GDR2 scaled position differences (Section \ref{['sec:cal-dr32']}). The colors indicate the median correction within each Healpix level 6 bin.
• Figure 5: Z-scores of corrected GDR3--GDR2 scaled position differences compared to GDR3 proper motions.