Differentiable Modeling of Planet and Substellar Atmosphere: High-resolution Emission, Transmission, and Reflection Spectroscopy with ExoJAX2

Differentiable Modeling of Planet and Substellar Atmosphere: High-resolution Emission, Transmission, and Reflection Spectroscopy with ExoJAX2

Modeling based on differentiable programming holds great promise for astronomy, enabling advanced techniques such as gradient-based posterior sampling and optimization. This paradigm motivated us to develop ExoJAX , the first auto-differentiable spectrum model of exoplanets and brown dwarfs. ExoJAX...

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Bibliographic Details
Main Authors: Hajime Kawahara, Yui Kawashima, Shotaro Tada, Hiroyuki Tako Ishikawa, Ko Hosokawa, Yui Kasagi, Takayuki Kotani, Kento Masuda, Stevanus K. Nugroho, Motohide Tamura, Hibiki Yama, Daniel Kitzmann, Nicolas Minesi, Brett M. Morris
Format: Article
Language:English
Published: IOP Publishing 2025-01-01
Series:The Astrophysical Journal
Subjects:
Exoplanet atmospheres
High resolution spectroscopy
Brown dwarfs
Markov chain Monte Carlo
Online Access:https://doi.org/10.3847/1538-4357/adcba2
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Summary:Modeling based on differentiable programming holds great promise for astronomy, enabling advanced techniques such as gradient-based posterior sampling and optimization. This paradigm motivated us to develop ExoJAX , the first auto-differentiable spectrum model of exoplanets and brown dwarfs. ExoJAX directly calculates cross-sections as functions of temperature and pressure to minimize interpolation errors in high-dispersion spectra, although initial work focused on narrowband emission spectroscopy. Here, we introduce a fast, memory-efficient opacity algorithm and differentiable radiative transfer for emission, transmission, and reflection spectroscopy. In the era of data-rich JWST observations, retrieval analyses are often forced to bin high-resolution spectra due to computational bottlenecks. The new algorithm efficiently handles native-resolution data, preserving the full information content and dynamic range. The advances proposed in this paper enable broader applications, demonstrated by retrievals of GL 229B’s high-dispersion emission, WASP-39 b’s JWST mid-resolution transmission at original resolution ( R  ∼ 2700), and Jupiter’s reflection spectrum. We derive a C/O ratio for GL 229B consistent with its host star, constrain WASP-39 b’s radial velocity from molecular line structures, and infer Jupiter’s metallicity in line with previous estimates.
ISSN:1538-4357

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