2025/12/09 by Libralato, M., Bedin, L., Burgasser, A.
Physics and Astronomy · #Stellar, planetary, and galactic studies #Astronomy and Astrophysical Research #Scientific Research and Discoveries
paper · doi:10.48550/arxiv.2512.08533
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_\odot, 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.