arXiv subjects

Esther van Dijk

Publications and source records attributed to Esther van Dijk.

3 recordsLinked to original sources

arXiv2026

The effect of the atmospheric C/O ratio on interiors of hot Jupiters

The atmosphere is the outer boundary of a gas giant exoplanet's interior. Therefore, compositional changes in the atmosphere can affect interior inferences. Typically, only metallicity is considered in atmospheric boundary conditions, while other elemental ratios, in particular the C/O ratio, are assumed to be solar. In light of the observational constraints now achievable with JWST, this assumption might no longer be justified. In this work, we investigate the effect of the C/O ratio on atmospheric boundary conditions, interiors and radii of hot Jupiters. We construct an atmospheric boundary grid, consisting of one-dimensional atmospheric models in radiative-convective and thermochemical equilibrium. This grid is coupled to a static interior structure model at the radiative-convective boundary (RCB). Because in the temperature regime of hot Jupiters, the C/O ratio determines the dominant species in the atmosphere, it can significantly alter the opacity and, consequently, the pressure and temperature at the RCB. This temperature change propagates into the convective interior, thus affecting the calculated radius. The radius difference relative to a solar C/O-atmosphere significantly exceeds observed radius uncertainties of 3 per cent for planets with equilibrium temperatures $\gtrsim$ 1500 K and super-solar atmospheric metallicities. As an example, we demonstrate that, for WASP-19~b, higher C/O ratios result in higher inferred intrinsic temperatures. These results highlight the importance of treating atmospheric composition and interior structure as a coupled system. As atmospheric constraints improve, incorporating measured C/O ratios into atmospheric boundary conditions is necessary to obtain robust inferences of hot Jupiter interiors.

astro-ph.EP↗

arXiv2026

Alkali lines at extreme densities and their impact on giant planet interior structure

Alkali lines, in particular the sodium Na $D$ (5891$\AA$, 5897$\AA$) and potassium K $D$ (7667$\AA$, 7701$\AA$) resonance doublets, are dominant opacity sources in giant planets over a wide range of temperatures ($\gtrsim$1000K). Their strong pressure-broadened wings significantly influence the thermal structure of giant planets, especially at high pressures. Most detailed line-profile calculations have so far been limited to perturber densities up to $10^{21}$cm$^{-3}$. However, conditions in the deep atmospheres and interiors of giant planets can reach significantly higher densities, making the temperature gradients increasingly uncertain. We determined how physically consistent collisional broadening of the Na $D$ and K $D$ lines at extreme densities affects opacity calculations and consequently the inferred interior structure of giant planets. We computed detailed Na $D$ and K $D$ line profiles using unified line theory, extending to molecular hydrogen perturber densities of $n_{\rm H_2} = 5 \times 10^{22}$cm$^{-3}$, which translates to pressures up to $\sim$ 20kbar. The revised cross sections were incorporated into Rosseland mean opacity tables, which were then used to evaluate their effect on planetary thermal structures. At densities $n_{\rm H_2} > 10^{21}$cm$^{-3}$, the line profiles predicted by unified line theory exhibit significantly stronger wings than commonly used Voigt profiles, as well as density-dependent line shifts, which substantially increases Rosseland mean opacities. Consequently, the radiative-convective boundary of warm and hot giant planets can shift to lower pressures, producing warmer interior adiabats and increasing inferred core masses. We further find that Jupiter is unlikely to host a stable radiative layer at the present time or throughout most of its evolution, as the required Na and K abundances for this are well below observational constraints.

astro-ph.EP↗

arXiv2025

Retrieving interior properties of hot Jupiters with Love numbers and atmospheric measurements

Understanding exoplanet interiors is crucial for interpreting atmospheric observations and constraining their evolution and formation. However, due to limited observational constraints, interiors structures remain poorly understood. In this work, we investigate how new observational constraints, such as the Love number and atmospheric metallicity, improve our ability to characterize the interiors of hot Jupiters, planets for which Love number measurements are most feasible. We assess the precision required in Love number measurements to derive interior properties using both a simple two-layer homogeneous model and a more complex dilute core model. To account for observational uncertainties, we implement a retrieval framework. Our results show that accurately constraining core mass and bulk metallicity requires a high-precision Love number measurement, better than 40% for a homogeneous model and 15% for a dilute core model, along with an atmospheric metallicity measurement. We apply our retrieval framework to five planets with observed Love numbers, of which only WASP-19Ab has both an atmospheric metallicity constraint and a highly precise Love number measurement, with a precision of 12%. For this flagship planet, both models confirm the presence of a core, although we cannot yet distinguish between a compact core or diluted core. With the homogeneous model, we find a core mass fraction of $0.21^{+0.05}_{-0.04}$, corresponding to $79^{+21}_{-18}$ $M_\mathrm{earth}$. Upcoming JWST observations are expected to provide high-precision Love number measurements and precise atmospheric data, offering new insights into the structure and composition of gas giant interiors.

astro-ph.EP↗