HD 209458 planetary transits from Hipparcos photometry

During its 39-month mission, Hipparcos observed the star {{HD 209458} on 89 occasions. Five of these observations are shown to correspond to epochs of planetary transits, with a 2.3+/-0.4% mean decrease of flux in the Hp band being observed during the transits. As a result of the long temporal baseline of more than 8 years between the Hipparcos and radial velocity measurements, an accurate orbital period of P=3.524739+/- 0.000014 days can be derived from the Hipparcos photometric data. Based on observations made with the ESA Hipparcos astrometry satellite}