Spatially resolved eastward winds and rotation of HD 189733b

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.