Autodifferentiable Spectrum Model for High-dispersion Characterization of Exoplanets and Brown Dwarfs
Year: 2022
Type: article
Abstract: We present an autodifferentiable spectral modeling of exoplanets and brown dwarfs. This model enables a fully Bayesian inference of the high-dispersion data to fit the ab initio line-by-line spectral computation to the observed spectrum by combining it with the Hamiltonian Monte Carlo in recent probabilistic programming languages. An open-source code, ExoJAX ( https://github.com/HajimeKawahara/exojax ), developed in this study, was written in Python using the GPU/TPU compatible package for automatic differentiation and accelerated linear algebra, JAX. We validated the model by comparing it with existing opacity calculators and a radiative transfer code and found reasonable agreements for the output. As a demonstration, we analyzed the high-dispersion spectrum of a nearby brown dwarf, Luhman 16 A, and found that a model including water, carbon monoxide, and H2/He collision-induced absorption was well fitted to the observed spectrum (R = 105 and 2.28–2.30 μm). As a result, we found that T 0 = 1295 − 32 + 35 K at 1 bar and C/O = 0.62 ± 0.03, which is slightly higher than the solar value. This work demonstrates the potential of a full Bayesian analysis of brown dwarfs and exoplanets as observed by high-dispersion spectrographs and also directly imaged exoplanets as observed by high-dispersion coronagraphy.
Institutions: The University of Tokyo, RIKEN, The University of Osaka, University of Kansas, Centre National de la Recherche Scientifique, Université Paris-Saclay, CentraleSupélec, Laboratoire d'Énergétique Moléculaire et Macroscopique, Combustion, Sandia National Laboratories California, Sandia National Laboratories
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Awards: Investigation of planet formation process through the simulations of chemical and physical evolution of protoplanetary disks and observations of chemical composition of exoplanet atmospheres, Exploring Exoplanet Atmospheres with High Dispersion Coronagraphs, Orbital and surface evolution of exoplanets and its application to remote-sensing, Mapping Habitable Planetary Environments with Exoplanet Imaging
OpenAlex ID: W3170691163