We present precise z-band photometric time series spanning times of transit of the two exoplanets recently discovered by the SuperWASP collaboration. We find planetary radii of 1.44 +/- 0.08 R_J and 1.04 +/- 0.06 R_J for WASP-1b and WASP-2b, respectively. These error estimates include both random errors in the photometry and also the uncertainty in the stellar masses. Our results are 5 times more precise than the values derived from the discovery data alone. Our measurement of the radius of WASP-2b agrees with previously published models of hot Jupiters that include both a 20-M_Earth core of solid material and the effects of stellar insolation. In contrast, we find that the models cannot account for the large size of WASP-1b, even if the planet has no core. Thus, we add WASP-1b to the growing list of hot Jupiters that are larger than expected. This suggests that ``inflated'' hot Jupiters are more common than previously thought, and that any purported explanations involving highly unusual circumstances are disfavored.
@article{arxiv.astro-ph/0610589,
title = {Precise Radius Estimates for the Exoplanets WASP-1b and WASP-2b},
author = {David Charbonneau and Joshua N. Winn and Mark E. Everett and David W. Latham and Matthew J. Holman and Gilbert A. Esquerdo and Francis T. O'Donovan},
journal= {arXiv preprint arXiv:astro-ph/0610589},
year = {2014}
}