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. KeenanG.~R.~M. Miller, V. Moulds, C. Moutou, A.~J. Norton, D. Queloz, A. Santerne, E.~K. Simpson, I. Skillen, A.~M.~S. Smith, S. Udry, C.~A. Watson, R.~G. West, P.~J. Wheatley

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48 Citations (Scopus)


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 plusmn 0.000008 d, Transit Epoch T$_0$ = 2 455 342.9688 plusmn 0.0002 (HJD), of duration 0.1168 plusmn 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 plusmn 0.03 M$_J$ and a radius of R$_pl$ = 1.27 plusmn 0.04 R$_J$, resulting in a mean density of 0.14 plusmn 0.02 $$_J$. The stellar parameters are mass M$_⋆$ = 0.93 plusmn 0.03 M$_⊙$, radius R$_⋆$ = 0.895 plusmn 0.23 R$_⊙$, and age 9$^+3$$_-4$ Gyr. Only WASP-17b and WASP-31b have lower densities than WASP-39b, although they are slightly more massive and highly irradiated planets. From our spectral analysis, the metallicity of WASP-39 is measured to be [Fe/H] = -0.12 plusmn 0.1 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. Spectroscopic and photometric data are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr ( or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A40
Original languageEnglish
Pages (from-to)A40
JournalAstronomy and Astrophysics
Publication statusPublished - 1 Jul 2011


  • stars: individual: WASP-39, techniques: photometric, techniques: radial velocities, planetary systems


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