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 (marked just as “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). The red point shows the mass estimate from Kervella et al. (2020).