WASP-1: a lithium- and metal-rich star with an oversized planet

In this paper, we present our results of a comprehensive spectroscopic analysis of WASP-1, the host star to the exoplanet WASP-1b. We derive T-eff = 6110 +/- 45 K, log g = 4.28 +/- 0.15 and [M/H] = 0.23 +/- 0.08, and also a high abundance of lithium, log n(Li) = 2.91 +/- 0.05. These parameters suggest an age for the system of 1-3 Gyr and a stellar mass of 1.25 -1.35 M-circle dot. This means that WASP-1 has properties very similar to those of HD 149026, the host star for the highest density planet yet detected. Moreover, their planets orbit at comparable distances and receive comparable irradiating fluxes from their host stars. However, despite the similarity of WASP-1 with HD 149026, their planets have strongly different densities. This suggests that gas giant planet density is not a simple function of host-star metallicity or of radiation environment at ages of similar to 2 Gyr.