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Probing the extreme planetary atmosphere of WASP-12b

Swain, Mark and Deroo, Pieter and Tinetti, Giovanna and Hollis, Morgan and Tessenyi, Marcell and Line, Michael and Kawahara, Hajime and Fujii, Yuka and Showman, Adam and Yurchenko, Sergey (2012) Probing the extreme planetary atmosphere of WASP-12b. . (Submitted)

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We report near-infrared measurements of the terminator region transmission spectrum and dayside emission spectrum of the exoplanet WASP-12b obtained using the HST WFC3 instrument. The disk-average dayside brightness temperature averages about 2900 K, peaking to 3200 K around 1.46 μm. Both the dayside and terminator region spectra can be explained in terms of opacity due to the metal hydrides CrH and TiH together with a dayside temperature inversion with a deep tropopause. Although our measurements do not constrain the C/O ratio, the combination of TiH and high temperatures could imply the atmosphere of WASP-12b may be significantly metal poor. The dayside flux distribution reconstructed from the ingress light-curve shape shows indications of a hotspot. If located along the equatorial plane, the possible hot spot is near the sub-stellar point, indicating the radiative time scale may be shorter than the advection time scale. We also find the near-infrared primary eclipse light curve is consistent with small amounts of prolate distortion. The likely picture of WASP-12b that emerges is that this gas giant is powerfully influenced by the parent star to the extent that the planet’s dayside atmosphere is star-like in terms of temperature, opacity, and the relative importance of radiation over advection. As part of the calibration effort for these data, we conducted a detailed study of instrument systematics using 65 orbits of WFC3-IR grims observations. The instrument systematics are dominated by detector-related affects, which vary significantly depending on the detector readout mode. The 256×256 subarray observations of WASP-12 produced measurements within 15% of the photon-noise limit using a simple calibration approach. Residual systematics are estimated to be ≤70 parts per million.

Item Type:Report or Paper (Discussion Paper)
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Line, Michael0000-0002-2338-476X
Additional Information:© 2012. All rights reserved. The research described in this publication was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Y.F. and H.K are supported by JSPS (Japan Society for the Promotion of Science) Fellowship for Research, DC:23-6070 and PD:22-5467, respectively. We thank Nikku Madhusudhan for kindly providing the data for a previously published theoretical model for comparison with these observations. We are grateful to Rachel Akeson and Thomas Green for useful discussions and suggestions on improving the manuscript.
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)DC:23-6070
Japan Society for the Promotion of Science (JSPS)PD:22-5467
Record Number:CaltechAUTHORS:20120604-080730050
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:31787
Deposited By: Tony Diaz
Deposited On:02 Aug 2012 18:56
Last Modified:20 Aug 2017 00:44

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