Wednesday, May 23, 2012

1205.4736 (Mark Swain et al.)

Probing the extreme planetary atmosphere of WASP-12b    [PDF]

Mark Swain, Pieter Deroo, Giovanna Tinetti, Morgan Hollis, Marcell Tessenyi, Michael Line, Hajime Kawahara, Yuka Fujii, Adam Showman, Sergey Yurchenko
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 {\mu}m. 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\times256 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 \leq70 parts per million.
View original: http://arxiv.org/abs/1205.4736

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