Proxima Centauri's Angular Diameter Revisited

Proxima Centauri is the nearest known exoplanet-hosting star and a benchmark for low-mass stellar models. Published diameters differ by several percent, affecting its inferred radius and temperature. The new analysis still awaits peer review, but it already lays out the central claim clearly.

The significance lies in exoplanet science has moved beyond the era of simple discovery into a period of comparative characterization. With more than five thousand confirmed planets known, the scientifically productive questions now concern atmospheric composition, internal structure, orbital history and the statistical properties of populations rather than the existence of individual worlds. A new detection or spectral measurement is most valuable when it adds a well-constrained data point to those comparative frameworks, not when it stands alone as an anecdote. The joint fit gives a uniform-disk angular diameter, $θ_{\rm UD}=1.117\pm0.024$ mas. Using the PHOENIX model and adopted bolometric flux, we obtain a PHOENIX limb-darkened angular diameter, $θ_{\rm LD, PHX}=1.154\pm0.026$ mas, a stellar radius, $R_\star=0.162\pm0.

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Have an idea for a project that will add value for arXiv's community. Published diameters differ by several percent, affecting its inferred radius and temperature.

Model-dependent near-infrared limb darkening introduces an additional 2-5% correction to the inferred radius. We re-reduced two previously published VLTI/PIONIER interferometric epochs from 2014 and combined them with three previously unpublished archival epochs from 2017 and 2019.

The broader interest lies in making the target less anecdotal and more comparable with the rest of the known planetary population. Population-level questions, such as the frequency of atmospheres around small rocky planets or the prevalence of water-rich worlds in the habitable zone, require well-characterized individual data points before statistical patterns become meaningful. Each new planet with a measured radius, mass and, ideally, atmospheric constraint is a brick in that larger structure, and the accumulation of bricks eventually allows theorists to test formation models against real distributions rather than projections.

We fit all five data sets jointly with uniform-disk and atmosphere-grid-based center-to-limb models. The joint fit gives a uniform-disk angular diameter, $\theta_{\rm UD}=1.117\pm0.024$ mas.

Because this is still a preprint, the result should be read with genuine interest and proportionate caution. Peer review is not a guarantee of correctness, but it is a process that forces authors to respond to technical criticism from specialists who have no stake in a particular outcome. Preprints that survive that process, often with substantive revisions, emerge with a stronger evidential base than the version that first appeared. Until that stage is complete, the responsible reading keeps uncertainty explicitly visible rather than treating the claims as established findings.

The next step is to improve independent constraints on the mass, radius, atmospheric composition and orbital dynamics of the target. Transmission spectroscopy with JWST, radial velocity campaigns with high-resolution ground-based spectrographs and phase-curve measurements from space photometry represent the observational toolkit that can move characterization from plausible to robust. That convergence of techniques is the standard the community now expects before a planetary atmosphere result is treated as confirmed. Until peer review and independent follow-up address those open questions, skepticism is not a failure of appreciation for the work; it is part of how science decides what to keep.

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