The Complete transmission spectrum of WASP-39b with a precise water constraint

28 Nov 2017  ·  Wakeford Hannah R., Sing David K., Deming Drake, Lewis Nikole K., Goyal Jayesh, Wilson Tom J., Barstow Joanna, Kataria Tiffany, Drummond Benjamin, Evans Thomas M., Carter Aarynn L., Nikolov Nikolay, Knutson Heather A., Ballester Gilda E., Mandell Avi M. ·

WASP-39b is a hot Saturn-mass exoplanet with a predicted clear atmosphere based on observations in the optical and infrared. Here we complete the transmission spectrum of the atmosphere with observations in the near-infrared (NIR) over three water absorption features with the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) G102 (0.8-1.1 microns) and G141 (1.1-1.7 microns) spectroscopic grisms... We measure the predicted high amplitude H2O feature centered at 1.4 microns, and the smaller amplitude features at 0.95 and 1.2 microns, with a maximum water absorption amplitude of 2.4 planetary scale heights. We incorporate these new NIR measurements into previously published observational measurements to complete the transmission spectrum from 0.3-5 microns. From these observed water features, combined with features in the optical and IR, we retrieve a well constrained temperature Teq = 1030(+30,-20) K, and atmospheric metallicity 151 (+48,-46)x solar which is relatively high with respect to the currently established mass-metallicity trends. This new measurement in the Saturn-mass range hints at further diversity in the planet formation process relative to our solar system giants. read more

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Earth and Planetary Astrophysics