![The black line shows the empirical high-S/N template spectrum of Proxima Centauri (left) and Barnard’s Star (right). In the top panel, the green curve shows the median spectrum obtained by taking the median flux at each wavelength across the full grid of PHOENIX M-dwarf spectra, while the shaded region denotes the corresponding 1σ envelope. Comparing this range of model spectra with the empirical M-dwarf spectra demonstrates that the PHOENIX models do not adequately reproduce the observed spectra. The middle and bottom panels show either empirical templates or postellar spectral samples constructed from synthetic SPIRou observations of the respective stars at different S/N regimes. For the postellar spectra, the 1σ, 2σ, and 3σ intervals are shown, highlighting the uncertainties recovered on individual spectral feature. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/09/POSTELLAR.png?fit=1200%2C680&ssl=1)
[astro-ph.EP] We present a novel approach to perform posterior sampling of the underlying stellar spectrum in high-resolution spectroscopic observations.
Our method, postellar, coherently combines information from empirical observations and physics-based models, enabling more accurate spectral recovery while providing uncertainties that can be propagated into downstream analyses.
This is accomplished by treating the intrinsic stellar spectrum as a latent variable and performing posterior sampling under a Gaussian likelihood with an informative prior constructed using a score-based diffusion model trained on PHOENIX stellar models.
We validate the framework on synthetic SPIRou radial velocity (RV) observations generated from the empirical spectra of Barnard’s Star and Proxima Centauri. Spectra inferred with postellar more accurately recover the ground truth than standard empirical templates.
or medium signal-to-noise observations, postellar improves RV accuracy by up to a factor of three, while RVs derived from empirical templates tend to be biased. This method performs particularly well in low signal-to-noise and low-cadence regimes.
The postellar framework is broadly applicable to other high-resolution spectroscopy science cases including stellar abundance analyses and exoplanet atmospheric characterization.
Dhvani Doshi, Nicolas B. Cowan, Yashar Hezaveh, Gabriel Missael Barco, Étienne Artigau
Comments: 24 pages, 7 figures, accepted in ApJ
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:2609.05599 [astro-ph.EP] (or arXiv:2609.05599v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2609.05599
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Submission history
From: Dhvani Doshi
[v1] Fri, 4 Sep 2026 18:00:00 UTC (11,586 KB)
https://arxiv.org/abs/2609.05599
Astrobiology,
