Proxima Centauri

Astrometric Reconnaissance of Exoplanetary Systems (ARES). I. Methodology Validation With HST Point-source Images Of Proxima Centauri

By Keith Cowing

Status Report

astro-ph.EP

December 16, 2025

Filed under astro-ph.EP, Astrometric Reconnaissance of Exoplanetary Systems (ARES), Astrometry, exoplanet, Gaia DR3 catalog, Gaia mission, Hubble Space Telescope, imaging, Proxima Centauri, Proxima Centauri b, Proxima centauri c, Proxima Centauri d, Stellar Cartography

Astrometric Reconnaissance of Exoplanetary Systems (ARES). I. Methodology Validation With HST Point-source Images Of Proxima Centauri — Expected mass of Proxima c as a function of its orbital radius derived from the PMa analysis. The solid blue line shows the mass estimate obtained in this work from the combination of HST and Gaia-DR3 astrometry, with the shaded light-blue region representing the 1σ uncertainty. The relation obtained combining Hip-Gaia (just “Hipparcos” in the plot legend for clarity) and part of the HST data is shown as a solid green line. The dashed yellow line represents the PMa-based relation obtained by Kervella et al. (2022) using Hipparcos and Gaia. The pink triangle marks the minimum mass derived of Proxima c from Damasso et al. (2020), while the red point shows the mass estimate from Kervella et al. (2020). — astro-ph.EP

We present the first results of the Astrometric Reconnaissance of Exoplanetary Systems (ARES) project, aimed at validating and characterizing candidate exoplanets around the nearest systems using multi-epoch Hubble Space Telescope (HST) data.

In this first paper, we focus on Proxima Centauri, leveraging archival and recent HST observations in point-source imaging mode. We refine the geometric-distortion calibration of the HST detector used, and develop a robust methodology to derive high-precision astrometric parameters by combining HST measurements with the Gaia DR3 catalog.

We determine Proxima’s position, proper motion, and parallax with uncertainties at the ∼0.4-mas, 50-μas yr⁻¹, and 0.2-mas level, respectively, achieving consistent results with what measured by Gaia within ∼1σ.

We further investigate the presence of the candidate exoplanet Proxima c by analyzing the proper-motion anomaly derived from combining long-term HST-based and short-term Gaia astrometry. Under the assumption of a circular, face-on orbit, we obtain an estimated mass of mc=3.4+5.2−3.4 M_⊙, broadly consistent with radial-velocity constraints but limited by our current uncertainties.

These results establish the foundation for the next phase of ARES, which will exploit HST spatial-scanning observations to achieve astrometric precisions of a few tens of μas and enable a direct search for astrometric signatures of low-mass companions.

M. Libralato, L. Bedin, A. Burgasser

Comments: 11 pages, 5 figures, 4 tables. Accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2512.08533 [astro-ph.EP](or arXiv:2512.08533v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2512.08533
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Submission history
From: Mattia Libralato
[v1] Tue, 9 Dec 2025 12:27:55 UTC (2,937 KB)
https://arxiv.org/abs/2512.08533
Astrobiology, exoplanet,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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