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

Southworth, J.; Dominik, M.; Jørgensen, U. G.; Rahvar, S.; Snodgrass, C.; Alsubai, K.; Bozza, V.; Browne, P.; Burgdorf, M.; Calchi Novati, S.; Dodds, P.; Dreizler, S.; Finet, F.; Gerner, T.; Hardis, S.; Harpsøe, 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.; Schäfer, S.; Schönebeck, F. and Surdej, J. (2011). A much lower density for the transiting extrasolar planet WASP-7. Astronomy & Astrophysics, 527, article no. A8.

DOI: https://doi.org/10.1051/0004-6361/201016183


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 ρJup versus 1.26+0.25−0.21 ρJup) and surface gravity (13.4 ± 2.6ms−2 versus 26.4+4.4−4.0 m s−2) 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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