Probing the extreme planetary atmosphere of WASP-12b
Abstract
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.
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.Attached Files
Submitted - 1205.4736.pdf
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Additional details
- Eprint ID
- 31787
- Resolver ID
- CaltechAUTHORS:20120604-080730050
- DC:23-6070
- Japan Society for the Promotion of Science (JSPS)
- PD:22-5467
- Japan Society for the Promotion of Science (JSPS)
- Created
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2012-08-02Created from EPrint's datestamp field
- Updated
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2023-06-02Created from EPrint's last_modified field