Lyman-α emission line of HD 189733 in April 2010 and September 2011. Spectra obtained before (black) and during the transits (blue) are displayed as a function of radial velocity relative to the star. The double-peaked profile results from a single stellar emission line absorbed at the center by interstellar hydrogen, which produces a broad absorption feature from about − 100 to +50 km s^-1. While no transit signatures are detected in 2010, two absorption regions are detected at more than 3-σduring the transit of 2011; these regions are plotted by gray zones. They are seen at the top of the red wing around +80 km s^-1 and, most significantly, in the blue wing with a ~100 km s^-1 wide absorption around −200 km s^-1.