Water dissociation and rotational broadening in the atmosphere of KELT-20 b from high-resolution spectroscopy
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arXiv
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| Natura: | Preprint |
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2025
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| author | Finnerty, Luke Xin, Yinzi Xuan, Jerry W. Inglis, Julie Fitzgerald, Michael P. Agrawal, Shubh Baker, Ashley Bartos, Randall Blake, Geoffrey A. Calvin, Benjamin Cetre, Sylvain Delorme, Jacques-Robert Doppmann, Greg Echeverri, Daniel Horstman, Katelyn Hsu, Chih-Chun Jovanovic, Nemanja Liberman, Joshua López, Ronald A. Martin, Emily C. Mawet, Dimitri Morris, Evan Pezzato, Jacklyn Ruffio, Jean-Baptiste Sappey, Ben Schofield, Tobias Skemer, Andew venenciano, Taylor Wallace, J. Kent Wallack, Nicole L. Wang, Jason J. Wang, Ji |
| author_facet | Finnerty, Luke Xin, Yinzi Xuan, Jerry W. Inglis, Julie Fitzgerald, Michael P. Agrawal, Shubh Baker, Ashley Bartos, Randall Blake, Geoffrey A. Calvin, Benjamin Cetre, Sylvain Delorme, Jacques-Robert Doppmann, Greg Echeverri, Daniel Horstman, Katelyn Hsu, Chih-Chun Jovanovic, Nemanja Liberman, Joshua López, Ronald A. Martin, Emily C. Mawet, Dimitri Morris, Evan Pezzato, Jacklyn Ruffio, Jean-Baptiste Sappey, Ben Schofield, Tobias Skemer, Andew venenciano, Taylor Wallace, J. Kent Wallack, Nicole L. Wang, Jason J. Wang, Ji |
| contents | We present atmospheric retrievals from Keck/KPIC phase II observations of the ultra-hot Jupiter KELT-20/MASCARA-2~b. Previous free retrievals of molecular abundances for ultra-hot Jupiters have been impacted by significant model biases due to variations in vertical abundance profiles, which we address by including molecular dissociation into our retrieval framework as an additional free parameter. We measure the abundance of CO ($\rm \log CO_{MMR} = -2.5^{+0.6}_{-0.5}$) and obtain a lower limit on the abundance of H$_2$O ($\rm \log H{_2}O_{MMR} = -1.5^{+0.8}_{-1.0}$, $>-3.0$ at 95\% confidence) in the atmosphere of \keltb. These abundances yield an atmospheric $\rm C/O = 0.1^{+0.4}_{-0.1}$ ($\rm C/O < 0.9$ at 95\% confidence) and suggest a metallicity approximately solar to $10\times$ solar. H$_2$O is dissociated at pressures below $\log P_{\rm H_2O} = -1.2^{+0.5}_{-0.7}$ bar, roughly consistent with predictions from chemical equilibrium models, and suggesting that the retrieved composition is not a result of assumptions about the vertical mixing profiles. We also constrain the rotational velocity of \keltb\ to $v\sin i = 7.5\pm0.7$ \kms, suggesting the presence of a jet comparable to the sound speed in the direction of the planet's rotation, assuming the actual rotation of the planet is tidally locked. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_01946 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Water dissociation and rotational broadening in the atmosphere of KELT-20 b from high-resolution spectroscopy Finnerty, Luke Xin, Yinzi Xuan, Jerry W. Inglis, Julie Fitzgerald, Michael P. Agrawal, Shubh Baker, Ashley Bartos, Randall Blake, Geoffrey A. Calvin, Benjamin Cetre, Sylvain Delorme, Jacques-Robert Doppmann, Greg Echeverri, Daniel Horstman, Katelyn Hsu, Chih-Chun Jovanovic, Nemanja Liberman, Joshua López, Ronald A. Martin, Emily C. Mawet, Dimitri Morris, Evan Pezzato, Jacklyn Ruffio, Jean-Baptiste Sappey, Ben Schofield, Tobias Skemer, Andew venenciano, Taylor Wallace, J. Kent Wallack, Nicole L. Wang, Jason J. Wang, Ji Earth and Planetary Astrophysics We present atmospheric retrievals from Keck/KPIC phase II observations of the ultra-hot Jupiter KELT-20/MASCARA-2~b. Previous free retrievals of molecular abundances for ultra-hot Jupiters have been impacted by significant model biases due to variations in vertical abundance profiles, which we address by including molecular dissociation into our retrieval framework as an additional free parameter. We measure the abundance of CO ($\rm \log CO_{MMR} = -2.5^{+0.6}_{-0.5}$) and obtain a lower limit on the abundance of H$_2$O ($\rm \log H{_2}O_{MMR} = -1.5^{+0.8}_{-1.0}$, $>-3.0$ at 95\% confidence) in the atmosphere of \keltb. These abundances yield an atmospheric $\rm C/O = 0.1^{+0.4}_{-0.1}$ ($\rm C/O < 0.9$ at 95\% confidence) and suggest a metallicity approximately solar to $10\times$ solar. H$_2$O is dissociated at pressures below $\log P_{\rm H_2O} = -1.2^{+0.5}_{-0.7}$ bar, roughly consistent with predictions from chemical equilibrium models, and suggesting that the retrieved composition is not a result of assumptions about the vertical mixing profiles. We also constrain the rotational velocity of \keltb\ to $v\sin i = 7.5\pm0.7$ \kms, suggesting the presence of a jet comparable to the sound speed in the direction of the planet's rotation, assuming the actual rotation of the planet is tidally locked. |
| title | Water dissociation and rotational broadening in the atmosphere of KELT-20 b from high-resolution spectroscopy |
| topic | Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2503.01946 |