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. A. 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

Abstract
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 M_pl = 0.28 ± 0.03 M_J and a radius of R_pl = 1.27±0.04 R_J, resulting in a mean density of 0.14±0.02 ρ_J. 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.

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

Notes
Spectroscopic and photometric data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A40

Astronomy and Astrophysics
Volume 531, Page A40_1
July 2011

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