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Fig. 1


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.

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