HAT-P-26b: A Neptune-mass exoplanet with a well-constrained heavy element abundance

Creators: Wakeford, Hannah R.; Sing, David K.; Kataria, Tiffany; Deming, Drake; Nikolov, Nikolay; Lopez, Eric D.; Tremblin, Pascal; Amundsen, David S.; Lewis, Nikole K.; Mandell, Avi M.; Fortney, Jonathan J.; Knutson, Heather; Benneke, Björn; Evans, Thomas M.

Abstract

A correlation between giant-planet mass and atmospheric heavy elemental abundance was first noted in the past century from observations of planets in our own Solar System and has served as a cornerstone of planet-formation theory. Using data from the Hubble and Spitzer Space Telescopes from 0.5 to 5 micrometers, we conducted a detailed atmospheric study of the transiting Neptune-mass exoplanet HAT-P-26b. We detected prominent H_2O absorption bands with a maximum base-to-peak amplitude of 525 parts per million in the transmission spectrum. Using the water abundance as a proxy for metallicity, we measured HAT-P-26b's atmospheric heavy element content (4.8^(+21.5)_(-4.0) times solar). This likely indicates that HAT-P-26b's atmosphere is primordial and obtained its gaseous envelope late in its disk lifetime, with little contamination from metal-rich planetesimals.

Additional Information

© 2017 American Association for the Advancement of Science. Received 30 June 2016; accepted 20 April 2017. This work is based on observations made with the NASA/European Space Agency (ESA) Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy under NASA contract NAS 5-26555. The HST and Spitzer data are available at http://mast.stsci.edu under project numbers GO-14110 (PI:Sing) and GO-14260 (PI:Deming) and at http://sha.ipac.caltech.edu under project number 90092 (P.I. Jean- Michel Désert). The combined transmission spectrum is available in Table 1. Support for this work was provided by NASA through grants under the HST-GO-14260 program from the STSci. H.R.W. acknowledges support from the NASA Postdoctoral Program, administered by Universities Space Research Association through a contract with NASA. Several authors acknowledge funding from the European Research Council under the European Union Seventh Framework Program: D.K.S., T.K., N.N., and T.M.E. under grant 336792; E.D.L. under grant 313014; and P.T. and D.S.A. under grant 247060-PEPS. The authors thank J. Goyal and B. Drummond for their contributions to the ATMO model framework. The authors thank the anonymous reviewers for their contribution to this paper, including the statistical reviewer who provided an interesting expansion and discussion.

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