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Title: C/O RATIO AS A DIMENSION FOR CHARACTERIZING EXOPLANETARY ATMOSPHERES

Abstract

Until recently, infrared observations of exoplanetary atmospheres have typically been interpreted using models that assumed solar elemental abundances. With the chemical composition fixed, attempts have been made to classify hot Jupiter atmospheres on the basis of stellar irradiation. However, recent observations have revealed deviations from predictions based on such classification schemes, and chemical compositions retrieved from some data sets have also indicated non-solar abundances. The data require a two-dimensional (2D) characterization scheme with dependence on both irradiation and chemistry. In this work, we suggest the carbon-to-oxygen (C/O) ratio as an important second dimension for characterizing exoplanetary atmospheres. In hot-hydrogen-dominated atmospheres, the C/O ratio critically influences the relative concentrations of several spectroscopically dominant species. Between a C/O of 0.5 (solar value) and 2, the H{sub 2}O and CH{sub 4} abundances can vary by several orders of magnitude in the observable atmosphere, and new hydrocarbon species such as HCN and C{sub 2}H{sub 2} become prominent for C/O {>=} 1, while the CO abundance remains almost unchanged. Furthermore, a C/O {>=} 1 can preclude a strong thermal inversion due to TiO and VO in a hot Jupiter atmosphere, since TiO and VO are naturally underabundant for C/O {>=} 1. We, therefore, suggest amore » new 2D classification scheme for hydrogen-dominated exoplanetary atmospheres with irradiation (or temperature) and C/O ratio as the two dimensions. We define four classes in this 2D space (O1, O2, C1, and C2) with distinct chemical, thermal, and spectral properties. Based on the most recent observations, we characterize the thermal structure and C/O ratios of six hot Jupiters (XO-1b, CoRoT-2b, WASP-14b, WASP-19b, WASP-33b, and WASP-12b) in the framework of our proposed 2D classification scheme. While the data for several systems in our sample are consistent with C-rich atmospheres, new observations are required to conclusively constrain their C/O ratios in the day side as well as the terminator regions of their atmospheres. We discuss how observations using existing and forthcoming facilities can constrain C/O ratios in exoplanetary atmospheres.« less

Authors:
 [1]
  1. Department of Physics, Yale University, New Haven, CT 06511 (United States)
Publication Date:
OSTI Identifier:
22094069
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 758; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTRONOMY; ASTROPHYSICS; CARBON; CARBON MONOXIDE; CHEMICAL COMPOSITION; CHEMISTRY; ELEMENT ABUNDANCE; HYDROCYANIC ACID; HYDROGEN; INFRARED SPECTRA; JUPITER PLANET; METHANE; OXYGEN; PLANETARY ATMOSPHERES; SATELLITE ATMOSPHERES; TEMPERATURE INVERSIONS; TITANIUM OXIDES; VANADIUM OXIDES; WATER

Citation Formats

Madhusudhan, Nikku, and Department of Astronomy, Yale University, New Haven, CT 06511. C/O RATIO AS A DIMENSION FOR CHARACTERIZING EXOPLANETARY ATMOSPHERES. United States: N. p., 2012. Web. doi:10.1088/0004-637X/758/1/36.
Madhusudhan, Nikku, & Department of Astronomy, Yale University, New Haven, CT 06511. C/O RATIO AS A DIMENSION FOR CHARACTERIZING EXOPLANETARY ATMOSPHERES. United States. https://doi.org/10.1088/0004-637X/758/1/36
Madhusudhan, Nikku, and Department of Astronomy, Yale University, New Haven, CT 06511. Wed . "C/O RATIO AS A DIMENSION FOR CHARACTERIZING EXOPLANETARY ATMOSPHERES". United States. https://doi.org/10.1088/0004-637X/758/1/36.
@article{osti_22094069,
title = {C/O RATIO AS A DIMENSION FOR CHARACTERIZING EXOPLANETARY ATMOSPHERES},
author = {Madhusudhan, Nikku and Department of Astronomy, Yale University, New Haven, CT 06511},
abstractNote = {Until recently, infrared observations of exoplanetary atmospheres have typically been interpreted using models that assumed solar elemental abundances. With the chemical composition fixed, attempts have been made to classify hot Jupiter atmospheres on the basis of stellar irradiation. However, recent observations have revealed deviations from predictions based on such classification schemes, and chemical compositions retrieved from some data sets have also indicated non-solar abundances. The data require a two-dimensional (2D) characterization scheme with dependence on both irradiation and chemistry. In this work, we suggest the carbon-to-oxygen (C/O) ratio as an important second dimension for characterizing exoplanetary atmospheres. In hot-hydrogen-dominated atmospheres, the C/O ratio critically influences the relative concentrations of several spectroscopically dominant species. Between a C/O of 0.5 (solar value) and 2, the H{sub 2}O and CH{sub 4} abundances can vary by several orders of magnitude in the observable atmosphere, and new hydrocarbon species such as HCN and C{sub 2}H{sub 2} become prominent for C/O {>=} 1, while the CO abundance remains almost unchanged. Furthermore, a C/O {>=} 1 can preclude a strong thermal inversion due to TiO and VO in a hot Jupiter atmosphere, since TiO and VO are naturally underabundant for C/O {>=} 1. We, therefore, suggest a new 2D classification scheme for hydrogen-dominated exoplanetary atmospheres with irradiation (or temperature) and C/O ratio as the two dimensions. We define four classes in this 2D space (O1, O2, C1, and C2) with distinct chemical, thermal, and spectral properties. Based on the most recent observations, we characterize the thermal structure and C/O ratios of six hot Jupiters (XO-1b, CoRoT-2b, WASP-14b, WASP-19b, WASP-33b, and WASP-12b) in the framework of our proposed 2D classification scheme. While the data for several systems in our sample are consistent with C-rich atmospheres, new observations are required to conclusively constrain their C/O ratios in the day side as well as the terminator regions of their atmospheres. We discuss how observations using existing and forthcoming facilities can constrain C/O ratios in exoplanetary atmospheres.},
doi = {10.1088/0004-637X/758/1/36},
url = {https://www.osti.gov/biblio/22094069}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 758,
place = {United States},
year = {2012},
month = {10}
}