LOOKING FOR GIANT EARTHS IN THE HD 209458 SYSTEM: A SEARCH FOR TRANSITS

We havemade a comprehensive transit search for exoplanets down to about 2 Earth radii in the HD 209458 system, based on nearly uninterrupted broadband optical photometry obtained with theMOST (Microvariability and Oscilla-tions of Stars) satellite, spanning 14 days in 2004 and 44 days in 2005.We have searched these data for limb-darkened transits at periods other than that of the known giant planet, from about 0.5 days to 2 weeks. Monte Carlo statistical tests of the data with synthetic transits inserted allow us to rule out additional close-in exoplanets with sizes rang-ing from about 0.20Y0.36 RJ (Jupiter radii), or 2.2Y4.0 R (Earth radii) on orbits whose planes are near that of HD 209458b. These null results constrain theories that invoke lower mass planets in orbits similar to HD 209458b to explain its anomalously large radius, and those that predict ‘‘hot Earths’ ’ due to the inward migration of HD 209458b. Subject headinggs: methods: data analysis — planetary systems 1