* Astronomy

Title: WASP-39b: a highly inflated Saturn-mass planet orbiting a late G-type star
Authors: Faedi, F.; Barros, S. C. C.; Anderson, D. R.; Brown, D. J. A.; Collier Cameron, A.; Pollacco, D.; Boisse, I.; Hebrard, G.; Lendl, M.; Lister, T. A.; Smalley, B.; Street, R. A.; Triaud, A. H. M. J.; Bento, J.; Butters, O. W.; Enoch, B.; Bouchy, F.; Haswell, C. A.; Hellier, C.; Keenan, F. P.; Miller, G. R. M.; Moulds, V.; Moutou, C.; Norton, A. J.; Queloz, D.; Santerne, A.; Simpson, E. K.; Skillen, I.; Smith, A. M. S.; Udry, S.; Watson, C. A.; West, R. G.; Wheatley, P. J.

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 T_{0}=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
pl=1.27±0.04~
j, resulting in a mean density of 0.14±0.02~
hoj. The stellar parameters are mass \mstar = 0.93±0.03\msun, radius
star = 0.895±0.23
sun, 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.

Read more (278kb, PDF)