Spectra of the Lyα line in the two brightest knots. The inner part of the line is contaminated by airglow. Additionally, the knot closer to the source (left panel) shows some emission on the red side of the line which could be due to scattered light from the central star (see text). We fit two Gaussians for knot and background (dashed line). Both knots appear blue-shifted by about 350 km s^-1.