Detection of a spectroscopic transit by the planet orbiting the star HD209458

We report the first detection of a planetary transit by spectroscopic measu rements. We have detected the distortion of the stellar line profiles durin g a planetary transit. With the ELODIE spectrograph we took a sequence of h igh precision radial velocities of the star HD209458 at time of a transit o f its planet. We detected an anomaly in the residuals of the orbit. The sha pe and the amplitude of the anomaly are modeled as a change of the mean ste llar line profile resulting from the planet crossing the disk of the rotati ng star. The planetary orbit is in the same direction as the stellar rotati on, Using the photometric transit to constrain the timing and the impact pa rameters of the transit, we measure an angle alpha = 3.9 [(0)] between the orbital plane and the apparent equatorial plane as well as a nu sin i=3.75 +/- 1.25 km s(-1). With additional constrains on the inclination of the sta r and on the statistics of the line of sight distribution, we can set an up per limit of 30 degrees to the angle between the orbital plane and the stel lar equatorial plane.