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Title: HELIOS–RETRIEVAL: An Open-source, Nested Sampling Atmospheric Retrieval Code; Application to the HR 8799 Exoplanets and Inferred Constraints for Planet Formation

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 consistentmore » 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).« less

Authors:
; ; ; ;  [1]; ; ;  [2];  [3];  [4]
  1. University of Bern, Space Research and Planetary Sciences, Sidlerstrasse 5, CH-3012, Bern (Switzerland)
  2. University of Bern, Center for Space and Habitability, Sidlerstrasse 5, CH-3012, Bern (Switzerland)
  3. Université Grenoble Alpes, IPAG, F-38000, Grenoble (France)
  4. Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290, Sauverny (Switzerland)
Publication Date:
OSTI Identifier:
22663267
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 154; Journal Issue: 3; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTRA; ABSORPTION SPECTROSCOPY; ALGORITHMS; CHEMISTRY; COMPARATIVE EVALUATIONS; EQUILIBRIUM; EXACT SOLUTIONS; GRAVITATIONAL INSTABILITY; LIMITING VALUES; PLANETS; RADIANT HEAT TRANSFER; SAMPLING; SATELLITE ATMOSPHERES; SATELLITES

Citation Formats

Lavie, Baptiste, Mendonça, João M., Malik, Matej, Demory, Brice-Olivier, Grimm, Simon L., Mordasini, Christoph, Oreshenko, Maria, Heng, Kevin, Bonnefoy, Mickaël, and Ehrenreich, David, E-mail: baptiste.lavie@space.unibe.ch, E-mail: kevin.heng@csh.unibe.ch. HELIOS–RETRIEVAL: An Open-source, Nested Sampling Atmospheric Retrieval Code; Application to the HR 8799 Exoplanets and Inferred Constraints for Planet Formation. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA7ED8.
Lavie, Baptiste, Mendonça, João M., Malik, Matej, Demory, Brice-Olivier, Grimm, Simon L., Mordasini, Christoph, Oreshenko, Maria, Heng, Kevin, Bonnefoy, Mickaël, & Ehrenreich, David, E-mail: baptiste.lavie@space.unibe.ch, E-mail: kevin.heng@csh.unibe.ch. HELIOS–RETRIEVAL: An Open-source, Nested Sampling Atmospheric Retrieval Code; Application to the HR 8799 Exoplanets and Inferred Constraints for Planet Formation. United States. doi:10.3847/1538-3881/AA7ED8.
Lavie, Baptiste, Mendonça, João M., Malik, Matej, Demory, Brice-Olivier, Grimm, Simon L., Mordasini, Christoph, Oreshenko, Maria, Heng, Kevin, Bonnefoy, Mickaël, and Ehrenreich, David, E-mail: baptiste.lavie@space.unibe.ch, E-mail: kevin.heng@csh.unibe.ch. Fri . "HELIOS–RETRIEVAL: An Open-source, Nested Sampling Atmospheric Retrieval Code; Application to the HR 8799 Exoplanets and Inferred Constraints for Planet Formation". United States. doi:10.3847/1538-3881/AA7ED8.
@article{osti_22663267,
title = {HELIOS–RETRIEVAL: An Open-source, Nested Sampling Atmospheric Retrieval Code; Application to the HR 8799 Exoplanets and Inferred Constraints for Planet Formation},
author = {Lavie, Baptiste and Mendonça, João M. and Malik, Matej and Demory, Brice-Olivier and Grimm, Simon L. and Mordasini, Christoph and Oreshenko, Maria and Heng, Kevin and Bonnefoy, Mickaël and Ehrenreich, David, E-mail: baptiste.lavie@space.unibe.ch, E-mail: kevin.heng@csh.unibe.ch},
abstractNote = {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).},
doi = {10.3847/1538-3881/AA7ED8},
journal = {Astronomical Journal (Online)},
number = 3,
volume = 154,
place = {United States},
year = {Fri Sep 01 00:00:00 EDT 2017},
month = {Fri Sep 01 00:00:00 EDT 2017}
}