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From dense hot Jupiter to low-density Neptune: The discovery of WASP-127b, WASP-136b, and WASP-138b

K. W. F. Lam, F. Faedi, D. Brown, D. R. Anderson, L. Delrez, M. Gillon, G. Hťbrard, M. Lendl, L. Mancini, J. Southworth, B. Smalley, A. H. M. J. Triaud, O. Turner, K. L. Hay, D. J. Armstrong, S. C. C. Barros, A. S. Bonomo, F. Bouchy, P. Boumis, A. Collier Cameron, A. P. Doyle, C. Hellier, T. Henning, E. Jehin, G. King, J. Kirk, T. Louden, P. F. L. Maxted, J. McCormac, H. P. Osborn, E. Palle, F. Pepe, D. Pollacco, J. Prieto-Arranz, D. Queloz, J. Rey, D. Sťgransan, S. Udry, S. R. Walker, R. G. West, P. J. Wheatley

Abstract
We report three newly discovered exoplanets from the SuperWASP survey. WASP-127b is a heavily inflated super-Neptune of mass 0.18±0.02 MJ and radius 1.37±0.04 RJ. This is one of the least massive planets discovered by the WASP project. It orbits a bright host star (Vmag=10.16) of spectral type G5 with a period of 4.17 days. WASP-127b is a low-density planet that has an extended atmosphere with a scale height of 2500±400 km, making it an ideal candidate for transmission spectroscopy. WASP-136b and WASP-138b are both hot Jupiters with mass and radii of 1.51±0.08 MJ and 1.38 ± 0.16 RJ, and 1.22±0.08 MJ and 1.09±0.05 RJ, respectively. WASP-136b is in a 5.22-day orbit around an F9 subgiant star with a mass of 1.41±0.07 M and a radius of 2.21±0.22 R. The discovery of WASP-136b could help constrain the characteristics of the giant planet population around evolved stars. WASP-138b orbits an F7 star with a period of 3.63 days. Its radius agrees with theoretical values from standard models, suggesting the presence of a heavy element core with a mass of ~10 M. The discovery of these new planets helps in exploring the diverse compositional range of short-period planets, and will aid our understanding of the physical characteristics of both gas giants and low-density planets.

Keywords
planetary systems; stars: individual: WASP-127; techniques: radial velocities; techniques: photometric; stars: individual: WASP-136; stars: individual: WASP-138; Astrophysics - Earth and Planetary Astrophysics

Astronomy and Astrophysics
Volume 599, Article Number A3, Number of pages 10
2017 March

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Instituto de Astrof√≠sica e Ci√™ncias do Espa√ßo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia