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A Hubble Space Telescope transit light curve for GJ 436b

By A. Reiners

Abstract

We present time series photometry for six partial transits of GJ 436b obtained with the Fine Guidance Sensor instrument on the Hubble Space Telescope (HST). Our analysis of these data yields independent estimates of the host star’s radius R⋆ = 0.505 +0.029 −0.020 R⊙, and the planet’s orbital period P = 2.643882 +0.000060 +0.21◦ −0.000058 d, orbital inclination i = 85.80◦ −0.25 ◦, mean central transit time Tc = 2454455.279241 +0.00026 −0.00025 HJD, and radius Rp = 4.90 +0.45 −0.33 R⊕. The radius we determine for the planet is larger than the previous findings from analyses of an infrared light curve obtained with the Spitzer Space Telescope. Although this discrepancy has a 92 % formal significance (1.7σ), it might be indicative of systematic errors that still influence the analyses of even the highest-precision transit light curves. Comparisons of all the measured radii to theoretical models suggest that GJ 436b has a H/He envelope of∼10 % by mass. W

Year: 2008
OAI identifier: oai:CiteSeerX.psu:10.1.1.312.875
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