We present high-precision photometry of two transit events of the extrasolar planetary system WASP-5 , obtained with the Danish 1.54 m telescope at ESO La Silla .
In order to minimise both random and flat-fielding errors , we defocussed the telescope so its point spread function approximated an annulus of diameter 40 pixels ( 16 ^ { \prime \prime } ) .
Data reduction was undertaken using standard aperture photometry plus an algorithm for optimally combining the ensemble of comparison stars .
The resulting light curves have point-to-point scatters of 0.50 mmag for the first transit and 0.59 mmag for the second .
We construct detailed signal to noise calculations for defocussed photometry , and apply them to our observations .
We model the light curves with the jktebop code and combine the results with tabulated predictions from theoretical stellar evolutionary models to derive the physical properties of the WASP-5 system .
We find that the planet has a mass of M _ { b } = 1.637 \pm 0.075 \pm 0.033 { M } _ { Jup } , a radius of R _ { b } = 1.171 \pm 0.056 \pm 0.012 { R } _ { Jup } , a large surface gravity of g _ { b } = 29.6 \pm 2.8 m s ^ { -2 } and a density of \rho _ { b } = 1.02 \pm 0.14 \pm 0.01 \rho _ { Jup } ( statistical and systematic uncertainties ) .
The planet ’ s high equilibrium temperature of T _ { eq } = 1732 \pm 80 K , makes it a good candidate for detecting secondary eclipses .