TY - JOUR
T1 - Toward More Reliable Analytic Thermochemical-equilibrium Abundances
AU - Cubillos, Patricio E.
AU - Blecic, Jasmina
AU - Dobbs-Dixon, Ian
N1 - Funding Information:
We thank the anonymous referee for his/her time and valuable comments. We thank contributors to the Python Programming Language (see Software below); the free and open-source community. This research has made use of NASA’s Astrophysics Data System Bibliographic Services. J.B. is supported by NASA through the NASA ROSES-2016/ Exoplanets Research Program, grant NNX17AC03G. We drafted this article using the aastex6.2 latex template (AAS Journals Team & Hendrickson 2018), with some further style modifications that are available at https://github.com/ pcubillos/ApJtemplate.
Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved.
PY - 2019/2/10
Y1 - 2019/2/10
N2 - Heng & Tsai developed an analytic framework to obtain thermochemical-equilibrium abundances for H 2 O, CO, CO 2 , CH 4 , C 2 H 2 , C 2 H 4 H , HCN, NH 3 , and N 2 for a system with known temperature, pressure, and elemental abundances (hydrogen, carbon, nitrogen, and oxygen). However, the implementation of their approach can become numerically unstable under certain circumstances, leading to inaccurate solutions (e.g., C/O≥1 atmospheres at low pressures). Building on their approach, we identified the conditions that prompt inaccurate solutions, and developed a new framework to avoid them, providing a reliable implementation for arbitrary values of temperature (200 to ∼2000 K), pressure (10-8 to 103 bar), and CNO abundances (10-3 to ∼10 2 × solar elemental abundances), for hydrogen-dominated atmospheres. The accuracy of our analytic framework is better than 10% for the more abundant species that have mixing fractions larger than 10-10, whereas the accuracy is better than 50% for the less abundant species. Additionally, we added the equilibrium-abundance calculation of atomic and molecular hydrogen into the system, and explored the physical limitations of this approach. Efficient and reliable tools, such as this one, are highly valuable for atmospheric Bayesian studies, which need to evaluate a large number of models.
AB - Heng & Tsai developed an analytic framework to obtain thermochemical-equilibrium abundances for H 2 O, CO, CO 2 , CH 4 , C 2 H 2 , C 2 H 4 H , HCN, NH 3 , and N 2 for a system with known temperature, pressure, and elemental abundances (hydrogen, carbon, nitrogen, and oxygen). However, the implementation of their approach can become numerically unstable under certain circumstances, leading to inaccurate solutions (e.g., C/O≥1 atmospheres at low pressures). Building on their approach, we identified the conditions that prompt inaccurate solutions, and developed a new framework to avoid them, providing a reliable implementation for arbitrary values of temperature (200 to ∼2000 K), pressure (10-8 to 103 bar), and CNO abundances (10-3 to ∼10 2 × solar elemental abundances), for hydrogen-dominated atmospheres. The accuracy of our analytic framework is better than 10% for the more abundant species that have mixing fractions larger than 10-10, whereas the accuracy is better than 50% for the less abundant species. Additionally, we added the equilibrium-abundance calculation of atomic and molecular hydrogen into the system, and explored the physical limitations of this approach. Efficient and reliable tools, such as this one, are highly valuable for atmospheric Bayesian studies, which need to evaluate a large number of models.
KW - methods: analytical
KW - planets and satellites: atmospheres
KW - planets and satellites: composition
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U2 - 10.3847/1538-4357/aafda2
DO - 10.3847/1538-4357/aafda2
M3 - Article
AN - SCOPUS:85062003610
SN - 0004-637X
VL - 872
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 111
ER -