We report the discovery of a low-density exoplanet transiting an 11th magnitude star in the Southern hemisphere. WASP-15b, which orbits its host star with a period P=3.7520656+-0.0000028d has a mass M_p=0.542+-0.050M_J and radius R_p=1.428+-0.077R_J, and is therefore the one of least dense transiting exoplanets so far discovered (rho_p=0.247+-0.035g cm^-3). An analysis of the spectrum of the host star shows it to be of spectral type around F5, with an effective temperature T_eff=6300+-100K and [Fe/H]=-0.17+-0.11.
@article{arxiv.0902.2651,
title = {The low density transiting exoplanet WASP-15b},
author = {R. G. West and D. R. Anderson and M. Gillon and L. Hebb and C. Hellier and P. F. L. Maxted and D. Queloz and B. Smalley and A. H. M. J. Triaud and D. M. Wilson and S. J. Bentley and A. Collier Cameron and B. Enoch and K. Horne and J. Irwin and T. A. Lister and M. Mayor and N. Parley and F. Pepe and D. Pollacco and D. Segransan and S. Udry and P. J. Wheatley},
journal= {arXiv preprint arXiv:0902.2651},
year = {2009}
}