The Metallicity and Carbon-to-oxygen Ratio of The Ultra-hot Jupiter WASP-76b from Gemini-S/IGRINS

By Keith Cowing
Status Report
May 17, 2024
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The Metallicity and Carbon-to-oxygen Ratio of The Ultra-hot Jupiter WASP-76b from Gemini-S/IGRINS
Cross-correlation signal-to-noise ratio (SNR) as a function of systemic velocity (Vsys) and planet Keplerian velocity (Kp) for detections of, from left to right, H2O, CO, and OH on night 1 (top), night 2 (middle) and from both nights combined (bottom). SNR is calculated following Equation 1 after performing a 3σ clipping using astropy.stats.sigma clipped stats. For the CO detection, we used only the orders containing the two distinct absorption bands near 1.61 and 2.45 µm. Black x marks denote the maximum cross-correlation in each plot, while white dashed lines indicate expected values for WASP-76b from previous studies (West et al. 2016; Gaia Collaboration et al. 2018). All three molecules are clearly detected in both nights of data, and the combined data set shows SNRs of 6.93, 6.47, and 3.90 for H2O, CO, and OH, respectively. The right-most column shows non-detections of HCN on each night and in the combined data set. — astro-ph.EP

Measurements of the carbon-to-oxygen (C/O) ratios of exoplanet atmospheres can reveal details about their formation and evolution.

Recently, high-resolution cross-correlation analysis has emerged as a method of precisely constraining the C/O ratios of hot Jupiter atmospheres. We present two transits of the ultra-hot Jupiter WASP-76b observed between 1.4-2.4 μm with Gemini-S/IGRINS. We detected the presence of H2O, CO, and OH at signal-to-noise rations of 6.93, 6.47, and 3.90, respectively. We performed two retrievals on this data set.

A free retrieval for abundances of these three species retrieved a volatile metallicity of [C+OH]=−0.70+1.27−0.93, consistent with the stellar value, and a super-solar carbon-to-oxygen ratio of C/O=0.80+0.07−0.11. We also ran a chemically self-consistent grid retrieval, which agreed with the free retrieval within 1σ but favored a slightly more sub-stellar metallicity and solar C/O ratio ([C+OH]=−0.74+0.23−0.17 and C/O=0.59+0.13−0.14).

A variety of formation pathways may explain the composition of WASP-76b. Additionally, we found systemic (Vsys) and Keplerian (Kp) velocity offsets which were broadly consistent with expectations from 3D general circulation models of WASP-76b, with the exception of a redshifted Vsys for H2O. Future observations to measure the phase-dependent velocity offsets and limb differences at high resolution on WASP-76b will be necessary to understand the H2O velocity shift.

Finally, we find that the population of exoplanets with precisely constrained C/O ratios generally trends toward super-solar C/O ratios. More results from high-resolution observations or JWST will serve to further elucidate any population-level trends.

Megan Weiner Mansfield, Michael R. Line, Joost P. Wardenier, Matteo Brogi, Jacob L. Bean, Hayley Beltz, Peter Smith, Joseph A. Zalesky, Natasha Batalha, Eliza M.-R. Kempton, Benjamin T. Montet, James E. Owen, Peter Plavchan, Emily Rauscher

Comments: 13 pages, 8 figures, 2 tables; accepted for publication in the Astronomical Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2405.09769 [astro-ph.EP] (or arXiv:2405.09769v1 [astro-ph.EP] for this version)
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Submission history
From: Megan Weiner Mansfield
[v1] Thu, 16 May 2024 02:20:36 UTC (1,369 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻