WASP-4b Transit Observations With GROND
Nikolay Nikolov, Thomas Henning, Johannes Koppenhoefer, Monika Lendl,, Gracjan Maciejewski, Jochen Greiner

TL;DR
This study used multiband ground-based transit observations to precisely determine the system parameters of the hot Jupiter WASP-4b, search for transit timing variations, and place constraints on potential additional bodies.
Contribution
First simultaneous multiband transit analysis of WASP-4b with high precision timing, providing updated system parameters and TTV constraints.
Findings
Planetary radius Rp = 1.413+/-0.020 RJup
No TTV signal greater than 20 seconds detected
Derived new ephemeris with high precision
Abstract
Ground-based simultaneous multiband transit observations allow an accurate system parameters determination and may lead to the detection and characterization of additional bodies via the transit timing variations (TTVs) method. We aimed to (i) characterize the heavily bloated WASP-4b hot Jupiter and its star by measuring system parameters and the dependence of the planetary radius as a function of four (Sloan g', r', i', z') wavelengths and (ii) search for TTVs. We recorded 987 images during three complete transits with the GROND instrument, mounted on the MPG/ESO-2.2m telescope at La Silla Observatory. Assuming a quadratic law for the stellar limb darkening we derive system parameters by fitting a composite transit light curve over all bandpasses simultaneously. To compute uncertainties of the fitted parameters, we employ the Bootstrap Monte Carlo Method. The three central transit…
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