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

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$20-35,000). We specifically retrieve [C/H], [O/H], and C/O and find them to be 0.55${}_{-0.39}^{+0.36}$, 0.47${}_{-0.32}^{+0.31}$, and 0.67${}_{-0.15}^{+0.12}$ 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.

19 pages, 6 figures, 3 tables, accepted to AAS journals

References in corpus (23)

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Cited by in corpus (14)

• Assessing the C/O Ratio Formation Diagnostic: A Potential Trend with Companion Mass
• Four-of-a-kind? Comprehensive atmospheric characterisation of the HR 8799 planets with VLTI/GRAVITY
• The ESO SupJup Survey III: Confirmation of 13CO in YSES 1 b and Atmospheric Detection of YSES 1 c with CRIRES+
• JWST-TST High Contrast: Living on the Wedge, or, NIRCam Bar Coronagraphy Reveals CO${}_2$ in the HR 8799 and 51 Eri Exoplanets' Atmospheres
• Rotation and Abundances of the Benchmark Brown Dwarf HD 33632 Ab from Keck/KPIC High-resolution Spectroscopy
• Fresh view of the hot brown dwarf HD 984 B through high-resolution spectroscopy
• Atmospheric characterization of the super-Jupiter HIP 99770 b with KPIC
• The compositions of the HR 8799 planets reflect accretion of both solids and metal-enriched gas
• Vortex Fiber Nulling for Exoplanet Observations: Implementation and First Light
• Impacts of high-contrast image processing on atmospheric retrievals
• CROCODILE \\ Incorporating medium-resolution spectroscopy of close-in directly imaged exoplanets into atmospheric retrievals via cross-correlation
• High-contrast spectroscopy with the new VLT/ERIS instrument: Molecular maps and radial velocity of the gas giant AF Lep b
• Distinct Rotational Evolution of Giant Planets and Brown Dwarf Companions
• Chemical Abundances Shape History (CASH). I. A Link between Giant Planets Orbital Periods and Host Stellar C/O Ratios