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HST hot-Jupiter transmission spectral survey: Clear skies for cool Saturn WASP-39b

Fischer, Patrick D. and Knutson, Heather A. and Sing, David K. and Henry, Gregory W. and Williamson, Michael W. and Fortney, Jonathan J. and Burrows, Adam S. and Kataria, Tiffany and Nikolov, Nikolay and Showman, Adam P. and Ballester, Gilda E. and Désert, Jean-Michel and Aigrain, Suzanne and Deming, Drake and Lecavelier des Etangs, Alain and Vidal-Madjar, Alfred (2016) HST hot-Jupiter transmission spectral survey: Clear skies for cool Saturn WASP-39b. Astrophysical Journal, 827 (1). Art. No. 19. ISSN 0004-637X. doi:10.3847/0004-637X/827/1/19.

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We present the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) optical transmission spectroscopy of the cool Saturn-mass exoplanet WASP-39b from 0.29-1.025 μm, along with complementary transit observations from Spitzer IRAC at 3.6 and 4.5 μm. The low density and large atmospheric pressure scale height of WASP-39b make it particularly amenable to atmospheric characterization using this technique. We detect a Rayleigh scattering slope as well as sodium and potassium absorption features; this is the first exoplanet in which both alkali features are clearly detected with the extended wings predicted by cloud-free atmosphere models. The full transmission spectrum is well matched by a clear H_2-dominated atmosphere, or one containing a weak contribution from haze, in good agreement with the preliminary reduction of these data presented in Sing et al. WASP-39b is predicted to have a pressure-temperature profile comparable to that of HD 189733b and WASP-6b, making it one of the coolest transiting gas giants observed in our HST STIS survey. Despite this similarity, WASP-39b appears to be largely cloud-free, while the transmission spectra of HD 189733b and WASP-6b both indicate the presence of high altitude clouds or hazes. These observations further emphasize the surprising diversity of cloudy and cloud-free gas giant planets in short-period orbits and the corresponding challenges associated with developing predictive cloud models for these atmospheres.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Knutson, Heather A.0000-0002-0822-3095
Sing, David K.0000-0001-6050-7645
Henry, Gregory W.0000-0003-4155-8513
Fortney, Jonathan J.0000-0002-9843-4354
Burrows, Adam S.0000-0002-3099-5024
Kataria, Tiffany0000-0003-3759-9080
Nikolov, Nikolay0000-0002-6500-3574
Désert, Jean-Michel0000-0002-0875-8401
Aigrain, Suzanne0000-0003-1453-0574
Deming, Drake0000-0001-5727-4094
Lecavelier des Etangs, Alain0000-0002-5637-5253
Additional Information:© 2016 American Astronomical Society. Received 2016 January 18; revised 2016 May 30; accepted 2016 June 1; published 2016 August 3. This work is based on observations with the NASA/ESA HST, obtained at the Space Telescope Science Institute (STScI) operated by AURA, Inc. This work is also based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Program (FP7/2007-2013)/ERC grant agreement no. 336792. Support for this work was provided by NASA through grants under the HST-GO-12473 program from the STScI. G.W.H. and M.H.W. acknowledge long-term support from Tennessee State University and the State of Tennessee through its Centers of Excellence program. We also thank the anonymous referee for suggestions that greatly improved this paper.
Funding AgencyGrant Number
European Research Council (ERC)336792
Tennessee State UniversityUNSPECIFIED
State of TennesseeUNSPECIFIED
Subject Keywords:planetary systems; planets and satellites: atmospheres; stars: individual (WASP-39) ; techniques: spectroscopic
Issue or Number:1
Record Number:CaltechAUTHORS:20160805-090053803
Persistent URL:
Official Citation:Patrick D. Fischer et al 2016 ApJ 827 19
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:69462
Deposited By: Ruth Sustaita
Deposited On:05 Aug 2016 16:33
Last Modified:11 Nov 2021 04:14

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