Updated parameters for the transiting exoplanet WASP-3b using RISE, a new fast camera for the Liverpool Telescope

Some of the first results are reported from RISE – a new fast camera mounted on the Liverpool Telescope primarily designed to obtain high time-resolution light curves of transiting extrasolar planets for the purpose of transit timing. A full and partial transit of WASP-3 are presented, and a Markov-Chain Monte Carlo analysis is used to update the parameters from the discovery paper. This results in a planetary radius of $1.29^{\rm +0.05}_{-0.12}$ RJ and therefore a density of $0.82^{+0.14}_{-0.09}~{\rho}_J$, consistent with previous results. The inclination is $85.06^{\rm +0.16}_{-0.15}$ deg, in agreement (but with a significant improvement in the precision) with the previously determined value. Central transit times are found to be consistent with the ephemeris given in the discovery paper; however, a new ephemeris calculated using the longer baseline results in $T_{\rm c}$(0) = 2 454 605.55915 $\pm$ 0.00023 HJD and P = 1.846835 $\pm$ 0.000002 days.