BeAR code runs exoplanet atmosphere retrievals on GPU: 17-parameter fit of WASP-77Ab in 14 minutes
Authors of the Bern code BeAR report GPU retrievals of high- and low-resolution exoplanet spectra; one forward model takes about 1 ms. Results for WASP-77Ab match published values.
A team describing the Bern Atmospheric Retrieval code (BeAR), the successor of Helios-r2, presented a GPU-based framework for retrieving exoplanet atmospheres from high-resolution, low-resolution and joint spectra. The work is an arXiv · preprint and has not yet been peer reviewed. The code is open source and available on GitHub arxiv.org
arXiv · препринтarxiv.orgOpen source ↗.
The authors tested it on dayside spectra of the hot Jupiter WASP-77Ab, taken with Gemini South/IGRINS and JWST/NIRSpec arxiv.org
arXiv · препринтarxiv.orgOpen source ↗.
How the framework works
BeAR performs joint retrievals by adding the log-likelihoods of high- and low-resolution data, both computed from the same model atmosphere arxiv.org
arXiv · препринтarxiv.orgOpen source ↗. The high-resolution part implements established cross-correlation log-likelihoods, with the line-depth scaling either fitted analytically or sampled as a free parameter. It also includes their per-pixel generalization, fast model filtering, and model re-injection adapted to that filtering
arxiv.org
arXiv · препринтarxiv.orgOpen source ↗.
The forward model and the likelihood run entirely on a graphics processing unit. One forward model takes about 1 ms on an NVIDIA GH200, which, according to the authors, allows millions of models per minute on a GPU cluster arxiv.org
arXiv · препринтarxiv.orgOpen source ↗. For comparison, an earlier retrieval of the IGRINS data of WASP-77Ab took about three days on 24 CPU cores and one GPU
arxiv.org
arXiv · препринтarxiv.orgOpen source ↗.
Results for WASP-77Ab
In separate retrievals of the IGRINS and NIRSpec spectra, BeAR reproduces published abundances, C/O ratios and metallicities to within 1.5 sigma. The preference for 13CO, the thermal structure and the line contrast agree to within 1 sigma arxiv.org
arXiv · препринтarxiv.orgOpen source ↗. The joint retrieval confirms a sub-solar metallicity and a near-solar C/O ratio
arxiv.org
arXiv · препринтarxiv.orgOpen source ↗.
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 arxiv.org
arXiv · препринтarxiv.orgOpen source ↗.
Injection–recovery tests show a limitation: the posteriors underestimate the uncertainties of abundance ratios by about a factor of two arxiv.org
arXiv · препринтarxiv.orgOpen source ↗. The authors note that high-resolution results depend on analysis choices, such as the removal of telluric and stellar lines, and therefore need to be checked with independent codes. Few open-source codes exist for this, and runtimes of hours to days make such checks expensive
arxiv.org
arXiv · препринтarxiv.orgOpen source ↗.
