Spectroscopic Evidence for a Temperature Inversion in the Dayside Atmosphere of Hot Jupiter WASP-33b

Creators: Haynes, Korey; Mandell, Avi M.; Madhusudhan, Nikku; Deming, Drake; Knutson, Heather

Abstract

We present observations of two occultations of the extrasolar planet WASP-33b using the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope, which allow us to constrain the temperature structure and composition of its dayside atmosphere. WASP-33b is the most highly irradiated hot Jupiter discovered to date, and the only exoplanet known to orbit a δ-Scuti star. We observed in spatial scan mode to decrease instrument systematic effects in the data, and removed fluctuations in the data due to stellar pulsations. The rms for our final, binned spectrum is 1.05 times the photon noise. We compare our final spectrum, along with previously published photometric data, to atmospheric models of WASP-33b spanning a wide range in temperature profiles and chemical compositions. We find that the data require models with an oxygen-rich chemical composition and a temperature profile that increases at high altitude. We find that our measured spectrum displays an excess in the measured flux toward short wavelengths that is best explained as emission from TiO. If confirmed by additional measurements at shorter wavelengths, this planet would become the first hot Jupiter with a thermal inversion that can be definitively attributed to the presence of TiO in its dayside atmosphere.

Additional Information

© 2015 The American Astronomical Society. Received 2015 February 5; Accepted 2015 May 1; Published 2015 June 12. The authors would like to thank the anonymous referee for thoughtful comments that improved the paper. 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., under NASA contract NAS 5-26555. These observations are associated with program GO-12495. Support for this work was provided by NASA through a grant from the Space Telescope Science Institute, with additional support for data analysis provided by a grant from the NASA Astrophysics Data Analysis Program(for K.H. and A.M.M.).

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