A Hubble Space Telescope Transit Light Curve For GJ 436B

dc.contributor.utaustinauthorBenedict, G. F.en_US
dc.creatorBean, J. L.en_US
dc.creatorBenedict, G. F.en_US
dc.creatorCharbonneau, D.en_US
dc.creatorHomeier, D.en_US
dc.creatorTaylor, D. C.en_US
dc.creatorMcArthur, B.en_US
dc.creatorSeifahrt, A.en_US
dc.creatorDreizler, S.en_US
dc.creatorReiners, A.en_US
dc.description.abstractWe 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-circle dot, and the planet's orbital period P = 2.643882(-0.000058)(+0.000060) d, orbital inclination i = 85.80 degrees(-0.25 degrees),(+ 0.21 degrees), mean central transit time T-c = 2 454 455.279241(-0.00025)(+0.00026) HJD, and radius Rp = 4.90(-0.33)(+ 0.45) R-circle plus. 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 (1.7s), 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 similar to 10% by mass. We point out the similarities in structure between this planet and Uranus and Neptune and discuss possible parallels between these planets' formation environments and dynamical evolution. We also find that the transit times for GJ 436b are constant to within 10s over the 11 planetary orbits that the HST data span. However, the ensemble of published values exhibits a long-term drift and our mean transit time is 128 s later than that expected from the Spitzer ephemeris. The sparseness of the currently available data hinders distinguishing between an error in the orbital period or perturbations arising from an additional object in the system as the cause of the apparent trend. Assuming the drift is due to an error in the orbital period we obtain an improved estimate for it of P = 2.643904 +/- 0.000005 d. This value and our measured transit times will serve as important benchmarks in future studies of the GJ 436 system.en_US
dc.identifier.citationBean, J. L., G. F. Benedict, D. Charbonneau, D. Homeier, D. C. Taylor, B. McArthur, A. Seifahrt, S. Dreizler, and A. Reiners. >A Hubble Space Telescope transit light curve for GJ 436b.> Astronomy & Astrophysics, Vol. 486, No. 3 (Aug., 2008): 1039-1046.en_US
dc.relation.ispartofserialAstronomy & Astrophysicsen_US
dc.rightsAdministrative deposit of works to Texas ScholarWorks: This works author(s) is or was a University faculty member, student or staff member; this article is already available through open access or the publisher allows a PDF version of the article to be freely posted online. The library makes the deposit as a matter of fair use (for scholarly, educational, and research purposes), and to preserve the work and further secure public access to the works of the University.en_US
dc.subjecttechniques : photometricen_US
dc.subjectstars : individual : gj 436en_US
dc.subjectstars :en_US
dc.subjectplanetary systemsen_US
dc.subjectextrasolar planet atmosphereen_US
dc.subjectneptune-mass planeten_US
dc.subjectm-dwarf gj-436en_US
dc.subjectastronomy & astrophysicsen_US
dc.titleA Hubble Space Telescope Transit Light Curve For GJ 436Ben_US

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