HST/FGS Photometry of Planetary Transits of HD 209458

Abstract

Abstract. We present the data, and modeling and analysis results from the photometric monitoring of five planetary transits of HD 209458 using the Fine Guidance Sensors (FGS) onboard the Hubble Space Telescope (HST). We have now included the output from all four FGS photometers in our data reduction and analysis increasing our S/N over our previous results. We have modeled the transits as an opaque spherical planet in a circular orbit about a limb darkened spherical star and simultaneously fit the model to the FGS data and published STIS transit data (Brown et al., 2001). The measured light curves show small features, a fraction of the transit depth. Some of these faint bumps and ripples appear to be real. We present an analysis of the FGS transit light curves, showing the results of the model fitting, a search for a possible planetary satellite, and an indication of which small features in the light curve we feel are not instrumental noise.