A survey of sodium absorption in ten giant exoplanets with high-resolution transmission spectroscopy

TL;DR

This survey of ten highly irradiated giant exoplanets using high-resolution transmission spectroscopy confirms sodium detections, explores atmospheric properties, and reveals common atmospheric dynamics, providing insights into exoplanet atmospheres.

Contribution

It presents a homogeneous analysis of sodium absorption in ten exoplanets, establishing empirical trends and measuring wind velocities, advancing understanding of atmospheric structure and dynamics.

Findings

Confirmed previous sodium detections in nine exoplanets and discovered one new detection.

Found that the relative atmospheric height decreases exponentially with a combined parameter of gravity and temperature.

Measured consistent blueshifted sodium lines indicating common atmospheric wind patterns.

Abstract

The alkali metal sodium (Na) is one of the most commonly detected chemical species in the upper atmospheres of giant exoplanets. In this work we conducted a homogeneous survey of Na in a diverse sample of ten highly irradiated giant exoplanets using high-resolution transmission spectroscopy. Our sample includes nine planets with previous Na detections and one new detection. We confirm previous detections and assess multiple approaches for deriving Na line properties from high-resolution transmission spectra. The homogeneously measured sodium line depths were used to constrain the atmospheric heights ($H_{\text{Na}}$) with respect to the planetary radii ($R_{\text{p}}$). We assess an empirical trend describing the relative atmospheric height ($H_{\text{Na}}/R_{\text{p}}$) as a function of planetary equilibrium temperature ($T_{\text{eq}}$) and surface gravity ($g$), in which $H_{\text{Na}}/R_{\text{p}}$ decreases exponentially with $\xi \propto gT_{\text{eq}}$, approaching a constant at large $\xi$. We also report the sodium D2/D1 line ratios across our sample and find that seven targets have line ratios that are consistent with unity. Finally, we measured net blueshifted offsets of the sodium absorption lines from their rest frame wavelengths for all ten planets, corresponding to day-night wind velocities of a few km s$^{-1}$. This suggests that the broad sample of exoplanets share common underlying processes that govern atmospheric dynamics. Our study highlights a promising avenue for using high-resolution transmission spectroscopy to further our understanding of how atmospheric characteristics vary over a diverse sample of exoplanets.