An extremely high photometric precision in ground-based observations of two transits in the WASP-50 planetary system

Abstract

We present photometric observations of two transits in the WASP-50 planetary system, obtained using the ESO New Technology Telescope and the defocused-photometry technique. The rms scatters for the two data sets are 258 and 211 ppm with a cadence of 170-200 s, setting a new record for ground-based photometric observations of a point source. The data were modelled and fitted using the PRISM and GEMC codes, and the physical properties of the system calculated. We find the mass and radius of the hot star to be 0.861 ± 0.057M⊙ and 0.855 ± 0.019 R⊙, respectively. For the planet we find a mass of 1.437 ± 0.068MJup, a radius of 1.138 ± 0.026 RJup and a density of 0.911 ± 0.033 ρJup. These values are consistent with but more precise than those found in the literature. We also obtain a new orbital ephemeris for the system: T0 = BJD/TDB 245 5558.612 37 (20) +1.955 0938(13) × E. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.