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Centro de Astrofísica da Universidade do Porto

Refined parameters and spectroscopic transit of the super-massive planet HD 147506b

B. Loeillet, A. Shporer, F. Bouchy, F. Pont, T. Mazeh, J.-L. Beuzit, I. Boisse, X. Bonfils, R. da Silva, X. Delfosse, M. Desort, A. Ecuvillon, T. Forveille, F. Galland, A. Gallenne, G. Hébrard, A.-M. Lagrange, C. Lovis, M. Mayor, C. Moutou, F. Pepe, C. Perrier, D. Queloz, D. Ségransan, J.-P. Sivan, N. C. Santos, Y. Tsodikovich, S. Udry, A. Vidal-Madjar

In this paper we report a refined determination of the orbital parameters and the detection of the Rossiter-McLaughlin effect of the recently discovered transiting exoplanet HAT-P-2b. The large orbital eccentricity and short orbital period of this exoplanet are unexpected and distinguish it from other known transiting exoplanets. We performed high precision radial velocity spectroscopic observations of HD147506 (HAT-P-2) with the new SOPHIE spectrograph, mounted on the 1.93 m telescope at OHP.We obtained 63 new measurements, including 35 on May 14th and 20 on June 11th, at nights that the planet was transiting its star. The RV anomaly observed illustrates that HAT-P-2b orbital motion is set in the same direction as its parent star spin. The sky-projected angle between the normal of the orbital plane and the stellar spin axis, λ = 0.0 ± 9.2◦, is consistent with zero. The planetary and stellar radii were re-determined: Rp = 0.952+0.020 −0.027 RJup, Rs = 1.412+0.029 −0.040 R⊙. The refined values of HAT-P-2b radius and mass (Mp = 8.64+0.29 −0.44 MJup) indicate a density of 12.41+0.42 −0.65 g cm−3, suggesting an object in between the known close-in planets with typical density of the order of 1 g cm−3, and the very low-mass stars, with density greater than 50 g cm−3.

Astronomy and Astrophysics
Volume 481, Page 529
April 2008

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