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

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 analyse the transmission spectrum around the Na D lines. We model the spectral signature of the RM-CL V -effect using synthetic PHOENIX spectra based on spherical LTE atmospheric models. We find an 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-1 and a moderate super-rotational streaming wind in the order of 3-4 km s-1, challenging claims of pre v ailing strong winds on HD 189733b.