Retrieving C and O Abundance of HR 8799 c by Combining High- and Low-Resolution Data

Ji Wang; Jason J. Wang; Jean-Baptiste Ruffio; Geoffrey A. Blake; Dimitri Mawet; Ashley Baker; Randall Bartos; Charlotte Z. Bond; Benjamin Calvin; Sylvain Cetre; Jacques-Robert Delorme; Greg Doppmann; Daniel Echeverri; Luke Finnerty; Michael P. Fitzgerald; Nemanja Jovanovic; Ronald Lopez; Emily C. Martin; Evan Morris; Jacklyn Pezzato; Sam Ragland; Garreth Ruane; Ben Sappey; Tobias Schofield; Andrew Skemer; Taylor Venenciano; J. Kent Wallace; Peter Wizinowich; Jerry W. Xuan; Marta L. Bryan; Arpita Roy; Nicole L. Wallack

doi:10.3847/1538-3881/ac9f19

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arXiv · 2209.15484

Retrieving C and O Abundance of HR 8799 c by Combining High- and Low-Resolution Data

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Abstract

The formation and evolution pathway for the directly-imaged multi-planetary system HR 8799 remains mysterious. Accurate constraints on the chemical composition of the planetary atmosphere(s) are key to solving the mystery. We perform a detailed atmospheric retrieval on HR 8799~c to infer the chemical abundances and abundance ratios using a combination of photometric data along with low- and high-resolution spectroscopic data (R$\sim$20-35,000). We specifically retrieve [C/H], [O/H], and C/O and find them to be 0.55$^{+0.36}_{-0.39}$, 0.47$^{+0.31}_{-0.32}$, and 0.67$^{+0.12}_{-0.15}$ at 68\% confidence. The super-stellar C and O abundances, yet a stellar C/O ratio, reveal a potential formation pathway for HR 8799~c. Planet c, and likely the other gas giant planets in the system, formed early on (likely within $\sim$1 Myr), followed by further atmospheric enrichment in C and O through the accretion of solids beyond the CO iceline. The enrichment either preceded or took place during the early phase of the inward migration to the planet current locations.

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Ji Wang, Jason J. Wang, Jean-Baptiste Ruffio, Geoffrey A. Blake, Dimitri Mawet, Ashley Baker, Randall Bartos, Charlotte Z. Bond, Benjamin Calvin, Sylvain Cetre, Jacques-Robert Delorme, Greg Doppmann, Daniel Echeverri, Luke Finnerty, Michael P. Fitzgerald, Nemanja Jovanovic, Ronald Lopez, Emily C. Martin, Evan Morris, Jacklyn Pezzato, Sam Ragland, Garreth Ruane, Ben Sappey, Tobias Schofield, Andrew Skemer, Taylor Venenciano, J. Kent Wallace, Peter Wizinowich, Jerry W. Xuan, Marta L. Bryan, Arpita Roy, Nicole L. Wallack. 2022-10-26. Retrieving C and O Abundance of HR 8799 c by Combining High- and Low-Resolution Data. https://doi.org/10.3847/1538-3881%2Fac9f19

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