A Search for Transit Effects in Spectra of 51 Pegasi and HD 209458

Abstract

We have used high-resolution optical spectra to search for obvious absorption or emission lines from the planets orbiting HD 209458 and 51 Pegasi. For each star, two spectra were obtained during inferior conjunction, enabling the detection of absorption lines from the planetary atmosphere. Spectra were also examined at a full range of orbital phases. The search involved subtracting spectra during transit from reference spectra taken out of transit. We found no signiÐcant variations in the spectra of HD 209458 and 51 Peg at any orbital phase, with typical detection thresholds of several percent. Velocity measurements of HD 209458 taken 40 minutes after midtransit fall D20 m s~1 below the Keplerian Ðt, presumably due to the planet removing Ñux from the receding hemisphere of the rotating stellar surface. This is consistent with the planet orbiting in the same direction as the star spins, in agreement with recent work by D. Queloz and coworkers.