A much lower density for the transiting extrasolar planet WASP-7

Authors :: Southworth, John
Dominik, M.
Jorgensen, U. G.
Rahvar, S.
Snodgrass, C.
Alsubai, K.
Bozza, V.
Browne, P.
Burgdorf, M.
Novati, S. Calchi
Dodds, P.
Dreizler, S.
Finet, F.
Gerner, T.
Hardis, S.
Harpsoe, K.
Hellier, C.
Hinse, T. C.
Hundertmark, M.
Kains, N.
Kerins, E.
Liebig, C.
Mancini, L.
Mathiasen, M.
Penny, M. T.
Proft, S.
Ricci, D.
Sahu, K.
Scarpetta, G.
Schafer, S.
Schonebeck, F.
Surdej, J.
Publication Year :: 2010
Abstract: 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/s2 versus 26.4 +4.4 -4.0 m/s2) 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.<br />Comment: Accepted for publication as a Research Note in A&A. 5 pages, 4 tables, 3 figures