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RE: WASP-7b
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Title: A High Stellar Obliquity in the WASP-7 Exoplanetary System
Authors: Simon Albrecht, Joshua N. Winn, R. Paul Butler, Jeffrey D. Crane, Stephen A Shectman, Ian B. Thompson, Teruyuki Hirano, Robert A. Wittenmyer

We measure a tilt of 866 deg between the sky projections of the rotation axis of the WASP-7 star, and the orbital axis of its close-in giant planet. This measurement is based on observations of the Rossiter-McLaughlin (RM) effect with the Planet Finder Spectrograph on the Magellan II telescope. The result conforms with the previously noted pattern among hot-Jupiter hosts, namely, that the hosts lacking thick convective envelopes have high obliquities. Because the planet's trajectory crosses a wide range of stellar latitudes, observations of the RM effect can in principle reveal the stellar differential rotation profile; however, with the present data the signal of differential rotation could not be detected. The host star is found to exhibit radial-velocity noise ('stellar jitter') with an amplitude of ~30m/s over a timescale of days.

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Posts: 131433
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WASP-7
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Title: A much lower density for the transiting extrasolar planet WASP-7
Authors: John Southworth, M. Dominik, U. G. Jorgensen, S. Rahvar, C. Snodgrass, K. Alsubai, V. Bozza, P. Browne, M. Burgdorf, S. Calchi Novati, P. Dodds, S. Dreizler, F. Finet, T. Gerner, S. Hardis, K. Harpsoe, C. Hellier, T. C. Hinse, M. Hundertmark, N. Kains, E. Kerins, C. Liebig, L. Mancini, M. Mathiasen, M. T. Penny, S. Proft, D. Ricci, K. Sahu, G. Scarpetta, S. Schafer, F. Schonebeck, J. Surdej

We present the first high-precision photometry of the transiting extrasolar planetary system WASP-7, obtained using telescope defocussing techniques and reaching a scatter of 0.68 mmag per point. We find that the transit depth is greater and that the host star is more evolved than previously thought. The planet has a significantly larger radius (1.330 0.093 Rjup versus 0.915 +0.046 -0.040 Rjup) and much lower density (0.41 0.10 rhojup versus 1.26 +0.25 -0.21 rhojup) and surface gravity (13.4 2.6 m/s versus 26.4 +4.4 -4.0 m/s) than previous measurements showed. Based on the revised properties it is no longer an outlier in planetary mass--radius and period--gravity diagrams. We also obtain a more precise transit ephemeris for the WASP-7 system.

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Date:
WASP-7b
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Title: WASP-7: The brightest transiting-exoplanet system in the Southern hemisphere
Authors: Coel Hellier, D.R. Anderson, M. Gillon, T.A. Lister, P.F.L. Maxted, D. Queloz, B. Smalley, A. Triaud, R.G. West, D.M. Wilson, K. Alsubai, S.J. Bentley, A. Collier Cameron, L. Hebb, K. Horne, J. Irwin, S.R. Kane, M. Mayor, F. Pepe, D. Pollacco, I. Skillen, S. Udry, P.J. Wheatley, D.J. Christian, R. Enoch, C.A. Haswell, Y.C. Joshi, A.J. Norton, R. Ryans, R.A. Street, I. Todd

We report that a Jupiter-mass planet, WASP-7b, transits the V = 9.5 star HD197286 every 4.95 d. This is the brightest discovery from the WASP-South transit survey and the brightest transiting-exoplanet system in the Southern hemisphere. WASP-7b is among the densest of the known Jupiter-mass planets, suggesting that it has a massive core. The planet mass is 0.96 M_Jup, the radius 0.915 R_Jup, and the density 1.26 rho_Jup.

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