Improved parameters for the transiting hot Jupiters WASP-4b and WASP-5b
Abstract
The gaseous giant planets WASP-4b and WASP-5b are transiting 12 magnitude solar-type stars in the Southern hemisphere. The aim of the present work is to refine the parameters of these systems using high cadence VLT/FORS2 z-band transit photometry and high resolution VLT/UVES spectroscopy. For WASP-4, the new estimates for the planet radius and mass from a combined analysis of our VLT data with previously published transit photometry and radial velocities are Rp = 1.30 +0.05-0.04 Rjup and Mp = 1.21 +0.13-0.08 Mjup, resulting in a density rhop = 0.55 +0.04-0.02 rhojup. The radius and mass for the host star are Rs = 0.87 +0.04-0.03 Rsun and Ms = 0.85 +0.11-0.07 Msun. Our ground-based photometry reaches 550 ppm at time sampling of ~50 seconds. Nevertheless, we also report the presence of an instrumental effect on the VLT that degraded our photometry for the WASP-5 observations. This effect could be a major problem for similar programs. Our new estimates for the parameters of the WASP-5 system are Rp = 1.09 +-0.07 Rjup, Mp = 1.58 +0.13-0.10 Mjup, rhop = 1.23 +0.26-0.16 rhojup, Rs = 1.03 +0.06-0.07 Rsun, and Ms = 0.96 +0.13-0.09 Msun. The measured size of WASP-5b agrees well with the basic models of irradiated planets, while WASP-4b is clearly an `anomalously' large planet.