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Abstract A primary goal of exoplanet science is to measure the atmospheric composition of gas giants in order to infer their formation and migration histories. Common diagnostics for planet formation are the atmospheric metallicity ([M/H]) and the carbon-to-oxygen (C/O) ratio as measured through transit or emission spectroscopy. The C/O ratio in particular can be used to approximately place a planet’s initial formation radius from the stellar host, but a given C/O ratio may not be unique to formation location. This degeneracy can be broken by combining measurements of both the C/O ratio and the atmospheric refractory-to-volatile ratio. We report the measurement of both quantities for the atmosphere of the canonical ultrahot Jupiter WASP-121 b using the high-resolution (R= 45,000) IGRINS instrument on Gemini South. Probing the planet’s direct thermal emission in both pre- and post-secondary eclipse orbital phases, we infer that WASP-121 b has a significantly superstellar C/O ratio of and a moderately superstellar refractory-to-volatile ratio at stellar. This combination is most consistent with formation between the soot line and H2O snow line, but we cannot rule out formation between the H2O and CO snow lines or beyond the CO snow line. We also measure velocity offsets between H2O, CO, and OH, potentially an effect of chemical inhomogeneity on the planet dayside. This study highlights the ability to measure both C/O and refractory-to-volatile ratios via high-resolution spectroscopy in the near-IRHandKbands.
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The Wanderer: Charting WASP-77A b’s Formation and Migration Using a System-wide Inventory of Carbon and Oxygen Abundances
Abstract 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 and12C/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 nonstellar C/O and13C 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 a12C/13C abundance analysis for host star WASP-77A (whose hot Jupiter’s12C/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 a12C/13C ratio of 51 ± 6 for WASP-77A, which is subsolar (∼91) but may still indicate13C 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 CO2snowlines and provide chemical evidence for the planet’s migration to its current location ∼0.024 au from its host star.
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- Award ID(s):
- 2108686
- PAR ID:
- 10548294
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 974
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 151
- Size(s):
- Article No. 151
- Sponsoring Org:
- National Science Foundation
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