Spatially resolved eastward winds and rotation of HD 189733b

TL;DR

This study measures the eastward wind velocities and rotation of the hot Jupiter HD 189733b using high-resolution spectra, revealing strong atmospheric eastward motion consistent with circulation models.

Contribution

It introduces a modeling approach that accounts for the Rossiter-McLaughlin effect, providing more accurate wind velocity measurements of HD 189733b's atmosphere.

Findings

Detected strong eastward atmospheric winds with specific velocity measurements.

Showed sodium absorption is velocity broadened, affecting previous interpretations.

Results align with predictions from atmospheric circulation models.

Abstract

We measure wind velocities on opposite sides of the hot Jupiter HD$\,$189733b by modeling sodium absorption in high-resolution HARPS transmission spectra. Our model implicitly accounts for the Rossiter-McLaughlin effect, which we show can explain the high wind velocities suggested by previous studies. Our results reveal a strong eastward motion of the atmosphere of HD$\,$189733b, with a redshift of $2.3^{+1.3}_{-1.5}$$\,$km$\,$s$^{-1}$ on the leading limb of the planet and a blueshift of $5.3^{+1.0}_{-1.4}$$\,$km$\,$s$^{-1}$ on the trailing limb. These velocities can be understood as a combination of tidally locked planetary rotation and an eastward equatorial jet; closely matching the predictions of atmospheric circulation models. Our results show that the sodium absorption of HD$\,$189733b is intrinsically velocity broadened and so previous studies of the average transmission spectrum are likely to have overestimated the role of pressure and thermal broadening.