The Wanderer: Charting WASP-77A b’s Formation and Migration Using a System-Wide Inventory of Carbon and Oxygen Abundances

The elemental and isotopic abundances of volatiles like carbon, oxygen, and nitrogen may trace a planet’s formation location relative to H₂O, CO₂, CO, NH₃, and N₂ “snowlines”, or the distance from the star at which these volatile elements sublimate.

By comparing the C/O and ¹²C/¹³C ratios measured in giant exoplanet atmospheres to complementary measurements of their host stars, we can determine whether the planet inherited stellar abundances from formation inside the volatile snowlines, or non-stellar C/O and ¹³C enrichment characteristic of formation beyond the snowlines.

To date, there are still only a handful of exoplanet systems where we can make a direct comparison of elemental and isotopic CNO abundances between an exoplanet and its host star.

Here, we present a ¹²C/¹³C abundance analysis for host star WASP-77A (whose hot Jupiter’s ¹²C/¹³C abundance was recently measured). We use MARCS stellar atmosphere models and the radiative transfer code TurboSpectrum to generate synthetic stellar spectra for isotopic abundance calculations. We find a ¹²C/¹³C ratio of 51±6 for WASP-77A, which is sub-solar (∼91) but may still indicate ¹³C-enrichment in its companion planet WASP-77A b (¹²C/¹³C = 26 ± 16, previously reported).

Together with the inventory of carbon and oxygen abundances in both the host and companion planet, these chemical constraints point to WASP-77A b’s formation beyond the H₂O and CO₂ snowlines and provide chemical evidence for the planet’s migration to its current location ∼0.024 AU from its host star.

David R. Coria, Neda Hejazi, Ian J. M. Crossfield, Maleah Rhem

Comments: 21 pages, 4 figures, 3 tables Accepted for publication in ApJ (8/14/2024)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2409.02286 [astro-ph.EP] (or arXiv:2409.02286v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2409.02286
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Related DOI:
https://doi.org/10.3847/1538-4357/ad7020
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Submission history
From: David Coria
[v1] Tue, 3 Sep 2024 20:47:41 UTC (4,109 KB)
https://arxiv.org/abs/2409.02286

Astrobiology, Astrochemistry,