The Search for Extended Atmospheres Around the Planets Orbiting 51 Peg and tau Boo.

The stars 51 Peg und tau Boo were observes with the high-resolution Utrecht Echelle Spectrograph (UES) on the 4.2 m William Herschel Telescope (WHT) on La Palma during the times the planets were due to transit in front of them and at times outside of the predicted transit periods. The results of a detailed comparison between on-transit and off-transit spectra to search for signatures of extended planetary atmospheres are presented and discussed. No evidenve of transient spectral features correlating with the predicted transit times were found. This project constitutes part of the 1998 La Palma International Time Programme on extrasolar planetary systems.