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WASP-39b: a highly inflated Saturn-mass planet orbiting a late G-type star

F. Faedi, S. C. C. Barros, D. R. Anderson, D. J. A. Brown, A. Collier Cameron, D. Pollacco, I. Boisse, G. Hébrard, M. Lendl, T. Lister, B. Smalley, R. A. Street, A. H. M. J. Triaud, J. Bento, F. Bouchy, O. W. Butters, B. Enoch, C. A. Haswell, C. Hellier, F. P. Keenan, G. R. M. Miller, V. Moulds, C. Moutou, A. J. Norton, D. Queloz, A. Santerne, E. Simpson, I. Skillen, A. M. S. Smith, S. Udry, C. A. Watson, R. G. West, P. J. Wheatley

We present the discovery of WASP-39b, a highly inflated transiting Saturn-mass planet orbiting a late G-type dwarf star with a period of 4.055259±0.000008 d, Transit Epoch T0 = 2455342.9688±0.0002(HJD), of duration 0.1168±0.0008 d. A combined analysis of the WASP photometry, high-precision follow up transit photometry and radial velocities yield a planetary mass of Mpl = 0.28 ± 0.03 MJ and a radius of Rpl = 1.27±0.04 RJ, resulting in a mean density of 0.14±0.02 ρJ. The stellar parameters are mass M = 0.93±0.03M, radius R = 0.895 ± 0.23R, and age 9+3-4 Gyr. Only WASP-17b and WASP-31b have lower densities than WASP-39b, although they are slightly more massive and highly irradiated planets. We measure, from our spectral analysis, the metallicity of WASP-39 to be [Fe/H]= -0.12±0.01 dex, and we find the planet to have an equilibrium temperature of 1116+33-32 K; both values strengthen the observed empirical correlation between these parameters and the planetary radius for the known transiting Saturn-mass planets.

planetary systems stars: individual: (WASP-39, GSC 04980-00761) - techniques: radial velocity, photometry

Spectroscopic and photometric data are only available at the CDS via anonymous ftp to ( or via

Astronomy & Astrophysics
Volume 531, Number of pages A40_1
2011 July

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia