Exoplanets & Exomoons

A Revisit Of The Mass-Metallicity Trends In Transiting Exoplanets

By Keith Cowing
Status Report
February 14, 2024
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A Revisit Of The Mass-Metallicity Trends In Transiting Exoplanets
The mass-metallicity correlation among planets, with the x-axis representing planet mass in Jupiter masses (MJ ) and the y-axis denoting normalized planetary abundance, both are in logarithmic scales. Our normalized H2O abundances are denoted by blue open circles, while the solid blue line represents the best-fit linear regression. The shaded blue region delineates the 1σ and 2σ quantiles. The trend depicted in W19 is shown by the dotted blue line, which exhibits a slightly more significant slope than ours. The linear model in our analysis is expressed as log(H2O) = -0.92+0.32 −0.33log(M/MJ ) – 0.90+0.21 −0.20. A recent detection of H2O from JWST/NIRISS for HAT-P-18b (Fu et al. 2022) is shown in the light purple circle in Figure 2. — astro-ph.EP

The two prevailing planet formation scenarios, core-accretion and disk instability, predict distinct planetary mass-metallicity relations. Yet, the detection of this trend remains challenging due to inadequate data on planet atmosphere abundance and inhomogeneities in both planet and host stellar abundance measurements.

Here we analyze high-resolution spectra for the host stars of 19 transiting exoplanets to derive the C, O, Na, S, and K abundances, including planetary types from cool mini-Neptunes to hot Jupiters (Teq ∼ 300 – 2700 K; planet radius ∼ 0.1 – 2 RJ). Our Monte Carlo simulations suggest that the current dataset, updated based on Welbanks et al. 2019, is unable to distinguish between a linear relation and an independent distribution model for the abundance-mass correlation for water, Na, or K.

To detect a trend with strong evidence (Bayes factor > 10) at the 2σ confidence interval, we recommend a minimum sample of 58 planets with HST measurements of water abundances coupled with [O/H] of the host stars, or 45 planets at the JWST precision. Coupled with future JWST or ground-based high resolution data, this well-characterized sample of planets with precise host star abundances constitute an important ensemble of planets to further probe the abundance-mass correlation.

Qinghui Sun, Sharon Xuesong Wang, Luis Welbanks, Johanna Teske, Johannes Buchner

Comments: 4 figures, 5 tables, accepted for publication in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2402.08292 [astro-ph.EP] (or arXiv:2402.08292v1 [astro-ph.EP] for this version)
Submission history
From: Qinghui Sun
[v1] Tue, 13 Feb 2024 08:47:31 UTC (307 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) 🖖🏻