2016/10/31 by Baptiste Lavie, B. Lavie, João M. Mendonça +11 · 3 citations
Earth and Planetary Sciences · Physics and Astronomy · #Accretion (finance) #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atmospheric Ozone and Climate #Exoplanet #Physics #Planet #Radiative transfer #Stellar, planetary, and galactic studies #astro-ph.EP #physics.ao-ph
paper · pdf · doi:10.3847/1538-3881/aa7ed8
published as AJ 154 91 (2017) · 27 pages, 21 figures, 3 tables, published in AJ
openalex publication_date 2017/08/11 · arxiv created 2017/08/21 · arxiv updated 2017/08/22 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Abstract We present an open-source retrieval code named HELIOS–RETRIEVAL , designed to obtain chemical abundances and temperature–pressure profiles by inverting the measured spectra of exoplanetary atmospheres. In our forward model, we use an exact solution of the radiative transfer equation, in the pure absorption limit, which allows us to analytically integrate over all of the outgoing rays. Two chemistry models are considered: unconstrained chemistry and equilibrium chemistry (enforced via analytical formulae). The nested sampling algorithm allows us to formally implement Occam’s Razor based on a comparison of the Bayesian evidence between models. We perform a retrieval analysis on the measured spectra of the four HR 8799 directly imaged exoplanets. Chemical equilibrium is disfavored for HR 8799b and c. We find supersolar C/H and O/H values for the outer HR 8799b and c exoplanets, while the inner HR 8799d and e exoplanets have a range of C/H and O/H values. The C/O values range from being superstellar for HR 8799b to being consistent with stellar for HR 8799c and being substellar for HR 8799d and e. If these retrieved properties are representative of the bulk compositions of the exoplanets, then they are inconsistent with formation via gravitational instability (without late-time accretion) and consistent with a core accretion scenario in which late-time accretion of ices occurred differently for the inner and outer exoplanets. For HR 8799e, we find that spectroscopy in the K band is crucial for constraining C/O and C/H. HELIOS–RETRIEVAL is publicly available as part of the Exoclimes Simulation Platform ( http://www.exoclime.org ).