An Open-source Bayesian Atmospheric Radiative Transfer (BART) Code. II. The TRANSIT Radiative Transfer Module and Retrieval of HAT-P-11b
Abstract
This and companion papers by Harrington et al. and Blecic et al. present the Bayesian Atmospheric Radiative Transfer (BART) code, an open-source, open-development package to characterize extrasolar planet atmospheres. BART combines a thermochemical equilibrium abundance (TEA), a radiative transfer (TRANSIT), and a Bayesian statistical (MC3) module to constrain atmospheric temperatures and molecular abundances for given spectroscopic observations. Here we describe the TRANSIT radiative transfer package, an efficient line-by-line radiative transfer C code for one-dimensional atmospheres, developed by P. Rojo and further modified by the UCF exoplanet group. This code produces transmission and hemisphere-integrated emission spectra. TRANSIT handles line-by-line opacities from HITRAN, Partridge & Schwenke (H2O), Schwenke (TiO), and Plez (VO) and collision-induced absorption from Borysow, HITRAN, and ExoMol. TRANSIT emission spectra models agree with models from C. Morley (private communication) within a few percent. We applied BART to the Spitzer and Hubble transit observations of the Neptune-sized planet HAT-P-11b. Our analysis of the combined HST and Spitzer data generally agrees with those from previous studies, finding atmospheric models with enhanced metallicity (≳100× solar) and high-altitude clouds (≲1 mbar level). When analyzing only the HST data, our models favor high-metallicity atmospheres, in contrast with the previous analysis by Chachan et al. We suspect that this discrepancy arises from the different choice of chemistry modeling (free constant-with-altitude versus thermochemical equilibrium) and the enhanced parameter correlations found when neglecting the Spitzer observations. The BART source code and documentation are available at https://github.com/exosports/BART.
- Publication:
-
The Planetary Science Journal
- Pub Date:
- April 2022
- DOI:
- 10.3847/PSJ/ac348b
- arXiv:
- arXiv:2104.12524
- Bibcode:
- 2022PSJ.....3...81C
- Keywords:
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- Exoplanet atmospheric composition;
- Astrostatistics techniques;
- Open source software;
- Planetary atmospheres;
- 2021;
- 1886;
- 1866;
- 1244;
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Instrumentation and Methods for Astrophysics
- E-Print:
- Accepted for publication at PSJ