Transmission spectroscopy of the inflated exoplanet WASP-52b, and evidence for a bright region on the stellar surface

Kirk, J.; Wheatley, P. J.; Louden, T.; Littlefair, S. P.; Copperwheat, C. M.; Armstrong, D. J.; Marsh, T. R.; Dhillon, V. S.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society, Volume 463, Issue 3, p.2922-2931

Advertised on:
12
2016
Number of authors
8
IAC number of authors
1
Citations
46
Refereed citations
44
Description
We have measured the transmission spectrum of the extremely inflated hot Jupiter WASP-52b using simultaneous photometric observations in Sloan Digital Sky Survey u', g' and a filter centred on the sodium doublet (Na I) with the ULTRACAM instrument mounted on the 4.2-m William Herschel Telescope. We find that Rayleigh scattering is not the dominant source of opacity within the planetary atmosphere and find a transmission spectrum more consistent with wavelength-independent opacity such as from clouds. We detect an in-transit anomaly that we attribute to the presence of stellar activity and find that this feature can be more simply modelled as a bright region on the stellar surface akin to solar faculae rather than spots. A spot model requires a significantly larger planet/star radius ratio than that found in previous studies. Our results highlight the precision that can be achieved by ground-based photometry with errors in the scaled planetary radii of less than one atmospheric scale height, comparable to Hubble Space Telescope observations.