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Published January 20, 2007 | Published
Journal Article Open

Using Stellar Limb-Darkening to Refine the Properties of HD 209458b


We use multiband photometry to refine estimates for the planetary radius and orbital inclination of the transiting planet system HD 209458. We gathered 1066 spectra over four distinct transits with the STIS spectrometer on the Hubble Space Telescope using two gratings with a resolution R = 1500 and a combined wavelength range of 290-1030 nm. We divide the spectra into 10 spectrophotometric bandpasses, five for each grating, of equal wavelength span within each grating, and fit a transit curve over all bandpasses simultaneously. In our fit we use theoretical values for the stellar limb-darkening to further constrain the planetary radius. We find that the radius of HD 209458b is (1.320 ± 0.025)R_(Jup), which is a factor of 2 more precise than current estimates. We also obtain improved estimates for the orbital period P and time of center of transit T_C. Although in principle the photon-limited precision of the STIS data should allow us to measure the timing of individual transits to a precision of 2-7 s, we find that uncertainties in the stellar limb-darkening coefficients and residual noise in the data degrade these measurements to a typical precision of ±14 s. Within this level of error, we find no significant variations in the timing of the eight events examined in this work.

Additional Information

© 2007 American Astronomical Society. Received 2006 March 20; accepted 2006 October 5. We are grateful to R. Kurucz for his assistance in calculating the limb-darkening for HD 209458. Support for program number HST-GO-09447 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by AURA under NASA contract NAS5-26555. H. K. was supported by a National Science Foundation Graduate Research Fellowship.

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