Helios-r2 -- A new Bayesian, open-source retrieval model for brown dwarfs and exoplanet atmospheres

Abstract

We present an improved, hybrid CPU-GPU atmospheric retrieval code, Helios-r2, which is applicable to medium-resolution emission spectra of brown dwarfs, in preparation for precision atmospheric spectroscopy in the era of the James Webb Space Telescope. The model is available as open-source code on the Exoclimes Simulation Platform. We subject Helios-r2 to a battery of tests of varying difficulty. The simplest test involves a mock retrieval on a forward model generated using the same radiative transfer technique, the same implementation of opacities, and the same chemistry model. The least trivial test involves a mock retrieval on synthetic spectra from the Sonora model grid, which uses a different radiative transfer technique, a different implementation of opacities, and a different chemistry model. A calibration factor, which is included to capture uncertainties in the brown dwarf radius, distance to the brown dwarf and flux calibration of the spectrum, may compensate, sometimes erroneously, for discrepancies in modeling choices and implementation. We analyze spectra of the benchmark brown dwarf GJ 570 D and the binary brown dwarf companions in the Epsilon Indi system. The retrieved surface gravities are consistent with previous studies and/or values inferred from dynamical masses (for Epsilon Indi Ba and Bb only). There remains no clear criterion on how to reject unphysical values of the retrieved brown dwarf radii. The inferred radii and corresponding masses should be taken with great caution. The retrieved carbon-to-oxygen ratios and metallicity depend on whether chemical equilibrium is assumed.

Accepted for publication in ApJ. The code is available under https://github.com/exoclime/Helios-r2

References in corpus (14)

• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Atmospheric Retrieval for Super-Earths: Uniquely Constraining the Atmospheric Composition with Transmission Spectroscopy
• Fingering convection and cloudless models for cool brown dwarf atmospheres
• ExoMol molecular line lists - XVI: The rotation-vibration spectrum of hot H${}_2$S
• A comparison of chemistry and dust cloud formation in ultracool dwarf model atmospheres
• Ammonia as a tracer of chemical equilibrium in the T7.5 dwarf Gliese 570D
• Uniform Atmospheric Retrieval Analysis of Ultracool Dwarfs I: Characterizing Benchmarks, Gl570D and HD3651B
• Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves
• Exploring Biases of Atmospheric Retrievals in Simulated JWST Transmission Spectra of Hot Jupiters
• Cloud structure of the nearest brown dwarfs: Spectroscopic variability of Luhman 16AB from the Hubble Space Telescope
• THOR: A New and Flexible Global Circulation Model to Explore Planetary Atmospheres
• Retrieval Analysis of the Emission Spectrum of WASP-12b: Sensitivity of Outcomes to Prior Assumptions and Implications for Formation History
• Supervised Machine Learning for Intercomparison of Model Grids of Brown Dwarfs: Application to GJ 570D and the Epsilon Indi B Binary System
• Discontinuous Galerkin finite element methods for radiative transfer in spherical symmetry

Cited by in corpus (4)

• The 2020 release of the ExoMol database: molecular line lists for exoplanet and other hot atmospheres
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• On the Chemical Abundance of HR 8799 and the Planet c
• Considerations for Atmospheric Retrieval of High-Precision Brown Dwarf Spectra