HD 209458 planetary transits from Hipparcos photometry

International audienceDuring 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 Hpband 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