We describe the discovery of HAT-P-4b, a low-density extrasolar planet transiting BD+36 2593, a V = 11.2 mag slightly evolved metal-rich late F star. The planet's orbital period is 3.056536+/-0.000057 d with a mid-transit epoch of 2,454,245.8154 +/- 0.0003 (HJD). Based on high-precision photometric and spectroscopic data, and by using transit light curve modeling, spectrum analysis and evolutionary models, we derive the following planet parameters: Mp= 0.68 +/- 0.04 MJ, Rp= 1.27 +/- 0.05 RJ, rho = 0.41 +/- 0.06 g cm-3 and a = 0.0446 +/- 0.0012 AU. Because of its relatively large radius, together with its assumed high metallicity of that of its parent star, this planet adds to the theoretical challenges to explain inflated extrasolar planets.
@article{arxiv.0710.0602,
title = {HAT-P-4b: A metal-rich low-density transiting hot Jupiter},
author = {G. Kovacs and G. A. Bakos and G. Torres and A. Sozzetti and D. W. Latham and R. W. Noyes and R. P. Butler and G. W. Marcy and D. A. Fischer and J. M. Fernandez and G. Esquerdo and D. D. Sasselov and R. P. Stefanik and A. Pal and J. Lazar and I. Papp and P. Sari},
journal= {arXiv preprint arXiv:0710.0602},
year = {2016}
}