Copperwheat, C. M., Wheatley, Peter J., Southworth, J. (John), Bento, J., Marsh, Tom, Dhillon, V. S., Fortney, J. J., Littlefair, S. P. and Hickman, R. D. G. (Richard D. G.) (2013) Transmission photometry of WASP-12b : simultaneous measurement of the planetary radius in three bands. Monthly Notices of the Royal Astronomical Society, Volume 434 (Number 1). pp. 661-670. doi:10.1093/mnras/stt1056 ISSN 0035-8711.

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Abstract

Transmission spectroscopy has been successfully used from both the ground and in space to characterize the atmospheres of transiting exoplanets. This technique is challenging from the ground because ground-based spectrographs tend not to be designed to be photometrically stable, and effects such as variable slit losses cause significant systematic uncertainties. An alternative approach is to use simultaneous photometric observations in multiple wavebands to determine wavelength-dependent transit depth differences. We report an application of this technique to one of the hottest known exoplanets, WASP-12b, using the triple-beam camera ULTRACAM. We obtained simultaneous light curves in Sloan u, and two narrow-band filters centred on 4169 and 6010 Å, with full widths at half-maximum 52 and 118 Å, respectively. We fit these light curves with a photometric model and determine the planetary radius in the three different bands. Our data show no evidence for a difference in planetary radius over the wavelength range we study, and are consistent with an atmosphere that is dominated by Rayleigh scattering from a high-altitude haze, as well as more complicated atmosphere models which include the effects of molecules such as TiO. Our planetary radius measurements have an average precision of 2.6 per cent, compared to the ̃1.4-2.4 per cent radius differences predicted by the models over this wavelength range. We also find a consistent time of ingress and egress across our three wavebands, in contrast to the early ingress which has been reported for this system at shorter wavelengths.

Item Type:	Journal Article
Divisions:	Faculty of Science, Engineering and Medicine > Science > Physics
Journal or Publication Title:	Monthly Notices of the Royal Astronomical Society
Publisher:	Oxford University Press
ISSN:	0035-8711
Official Date:	September 2013
Dates:	Date Event September 2013 Published
Volume:	Volume 434
Number:	Number 1
Page Range:	pp. 661-670
DOI:	10.1093/mnras/stt1056
Status:	Peer Reviewed
Publication Status:	Published
Access rights to Published version:	Restricted or Subscription Access

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