Spectral signature of atmospheric winds in high resolution transit observations

TL;DR

This paper models how atmospheric winds in hot and ultra-hot Jupiters affect sodium absorption lines during transit, revealing wind velocities and temperature effects that influence spectral line broadening.

Contribution

It introduces a model linking atmospheric wind speeds to sodium line broadening in high-resolution transit spectra of hot Jupiters, highlighting temperature-dependent wind dynamics.

Findings

High wind velocities can explain sodium line broadening observed in transit spectra.

Line broadening decreases with lower planetary equilibrium temperatures.

Ionization-induced atmospheric drag may slow winds on cooler hot Jupiters.

Abstract

The study of exoplanet atmospheres showed large diversity compared to the planets in our solar system. Especially Jupiter type exoplanets orbiting their host star in close orbits, the so-called hot and ultra-hot Jupiters, have been studied in detail due to their enhanced atmospheric signature. Due to their tidally locked status, the temperature difference between the day- and nightside triggers atmospheric winds which can lead to various fingerprints in the observations. Spatially resolved absorption lines during transit such as sodium (Na) could be a good tracer for such winds. Different works resolved the Na$^-$ absorption lines on different exoplanets which show different line widths. Assuming that this could be attributed to such zonal jet streams, this work models the effect of such winds on synthetic absorption lines. For this, transiting Jupiter type planets with rotational velocities similar to hot and ultra-hot Jupiter are considered. The investigation shows that high wind velocities could reproduce the broadening of Na-line profiles inferred in different high-resolution transit observations. There is a tendency that the broadening values decrease for planets with lower equilibrium temperature. This could be explained by atmospheric drag induced by the ionization of alkali lines which slow down the zonal jet streams, favoring their existence on hot Jupiter rather than ultra-hot Jupiter.