The PEPSI Exoplanet Transit Survey (PETS). V: New Na D transmission spectra indicate a quieter atmosphere on HD 189733b

TL;DR

This study presents high-resolution transmission spectra of HD 189733b around Na D lines, revealing a quieter atmosphere with weaker winds than previously claimed, and questions the planetary origin of some absorption features.

Contribution

It provides new high-resolution Na D transmission spectra and models the RM-CLV effect, offering insights into atmospheric winds and challenging prior assumptions about wind strength.

Findings

Na D absorption detected between second and third contact

Weak day-to-nightside wind of ~0.7 km/s inferred

Moderate super-rotational wind of 3-4 km/s suggested

Abstract

Absorption lines from exoplanet atmospheres observed in transmission allow us to study atmospheric characteristics such as winds. We present a new high-resolution transit time-series of HD 189733b, acquired with the PEPSI instrument at the LBT and analyze the transmission spectrum around the Na D lines. We model the spectral signature of the RM-CLV-effect using synthetic PHOENIX spectra based on spherical LTE atmospheric models. We find a Na D absorption signature between the second and third contact but not during the ingress and egress phases, which casts doubt on the planetary origin of the signal. Presupposing a planetary origin of the signal, the results suggest a weak day-to-nightside streaming wind in the order of 0.7 km/s and a moderate super-rotational streaming wind in the order of 3 - 4 km/s, challenging claims of prevailing strong winds on HD 189733b.