BeAR: The Bern Atmospheric Retrieval code - A GPU-accelerated framework for low-resolution, high-resolution, and joint retrievals of exoplanet atmospheres

@misc{wang2026bear,
  title = {{BeAR: The Bern Atmospheric Retrieval code - A GPU-accelerated framework for low-resolution, high-resolution, and joint retrievals of exoplanet atmospheres}},
  author = {Esther Wang and Daniel Kitzmann and H. Jens Hoeijmakers and Joost P. Wardenier and Helena Lecoq-Molinos},
  howpublished = {arXiv},
  year = {2026},
  month = nov,
  doi = {10.48550/arxiv.2611.08489},
  eprint = {2611.08489},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2611.08489},
}

TY  - UNPB
TI  - BeAR: The Bern Atmospheric Retrieval code - A GPU-accelerated framework for low-resolution, high-resolution, and joint retrievals of exoplanet atmospheres
AU  - Esther Wang
AU  - Daniel Kitzmann
AU  - H. Jens Hoeijmakers
AU  - Joost P. Wardenier
AU  - Helena Lecoq-Molinos
PY  - 2026
DA  - 2026/11/05
PB  - arXiv
DO  - 10.48550/arxiv.2611.08489
UR  - https://arxiv.org/abs/2611.08489
AB  - We present BeAR, the Bern Atmospheric Retrieval code and successor of Helios-r, and its new high-resolution cross-correlation framework for emission and transmission spectra. BeAR performs joint retrievals by adding the log-likelihoods of high- and low-resolution data computed from the same model atmosphere. The framework implements established cross-correlation log-likelihoods, with the line-depth scaling either fitted analytically or sampled as a free parameter, their per-pixel generalization, fast model filtering, and model re-injection adapted to this filtering. The forward model and likelihood run entirely on a graphics processing unit (GPU). One forward model takes about 1 ms on an NVIDIA GH200, allowing millions of models per minute on a GPU cluster. In separate retrievals of Gemini South/IGRINS and JWST/NIRSpec dayside spectra of the hot Jupiter WASP-77Ab, BeAR reproduces published abundances, C/O ratios, and metallicities to within 1.5 sigma, the preference for 13CO, and the thermal structure and line contrast to within 1 sigma. The joint retrieval confirms a sub-solar metallicity and a near-solar C/O ratio. A full IGRINS retrieval with 17 free parameters takes 27 to 42 minutes on a single NVIDIA GeForce RTX 5080 or about 14 minutes on eight RTX 4090 GPUs. Injection--recovery tests show that the posteriors underestimate the uncertainties of abundance ratios by about a factor of two.
ER  -