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The Complete Transmission Spectrum of WASP-39b with a Precise Water Constraint

Wakeford, H. R. and Sing, D. K. and Deming, D. and Lewis, N. K. and Goyal, J. and Wilson, T. J. and Barstow, J. and Kataria, T. and Drummond, B. and Evans, T. M. and Carter, A. L. and Nikolov, N. and Knutson, H. A. and Ballester, G. E. and Mandell, A. M. (2018) The Complete Transmission Spectrum of WASP-39b with a Precise Water Constraint. Astronomical Journal, 155 (1). Art. No. 29. ISSN 1538-3881.

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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 μm) and G141 (1.1–1.7 μm) spectroscopic grisms. We measure the predicted high-amplitude H_2O feature centered at 1.4 μm and the smaller amplitude features at 0.95 and 1.2 μm, 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 to 5 μm. From these observed water features, combined with features in the optical and IR, we retrieve a well constrained temperature T_(eq) = 1030_(-20)^(+30) K, and atmospheric metallicity 151_(-46)^(+48) 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Wakeford, H. R.0000-0003-4328-3867
Sing, D. K.0000-0001-6050-7645
Deming, D.0000-0001-5727-4094
Lewis, N. K.0000-0002-8507-1304
Barstow, J.0000-0003-3726-5419
Kataria, T.0000-0003-3759-9080
Drummond, B.0000-0001-7589-5484
Evans, T. M.0000-0001-5442-1300
Nikolov, N.0000-0002-6500-3574
Knutson, H. A.0000-0002-0822-3095
Mandell, A. M.0000-0002-8119-3355
Additional Information:© 2017. The American Astronomical Society. Received 2017 September 18; revised 2017 November 24; accepted 2017 November 27; published 2017 December 21. The authors thank K. B. Stevenson for useful discussions on the data analysis. This work is based on observations made with the NASA/ESA Hubble Space Telescope that were obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. These observations are associated with programs GO-14169 (PI. HR Wakeford) and GO-14260 (PI. D Deming). D.K.S., H.R.W., T.E., B.D., and N.N., acknowledge funding from the European Research Council (ERC) under the European Unions Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 336792. J.G. acknowledges support from Leverhulme Trust. A.L.C. acknowledges support from the STFC. H.R.W. also acknowledges support from the Giacconi Fellowship at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. This research has made use of NASA's Astrophysics Data System, and components of the IDL astronomy library, and the Python modules SciPy, NumPy, and Matplotlib. Many thanks go to the crew of STS-125 HST servicing mission 4, for fixing HST and for installing WFC3 over a period of 5 EVAs that took a total of 36 hr 56 minutes, almost matching the total exposure time taken by these observations. Also, thank you to Mac Time machine without which this project would not have been possible, due to multiple moves and hard-drive failures. Facility: HST (WFC3) - .
Group:Astronomy Department
Funding AgencyGrant Number
European Research Council (ERC)336792
Leverhulme TrustUNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
Giacconi FellowshipUNSPECIFIED
Subject Keywords:planets and satellites: atmospheres; planets and satellites: individual (WASP-39b) ; techniques: spectroscopic
Issue or Number:1
Record Number:CaltechAUTHORS:20171220-144541875
Persistent URL:
Official Citation:H. R. Wakeford et al 2018 AJ 155 29
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83994
Deposited By: George Porter
Deposited On:20 Dec 2017 23:18
Last Modified:20 Apr 2020 08:47

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