We report the discovery of a Jupiter-size planet transiting a relatively bright ( V = 11.56 ) and metal-rich early K dwarf star with a period of \sim 2.9 days .
On the basis of follow-up photometry and spectroscopy we determine the mass and radius of the planet , HAT-P-3b , to be M _ { p } = 0.599 \pm 0.026 M _ { Jup } and R _ { p } = 0.890 \pm 0.046 R _ { Jup } .
The relatively small size of the object for its mass implies the presence of about 75 M _ { \earth } worth of heavy elements ( \sim \frac { 1 } { 3 } of the total mass ) based on current theories of irradiated extrasolar giant planets , similar to the mass of the core inferred for the transiting planet HD 149026b .
The bulk density of HAT-P-3b is found to be \rho _ { p } = 1.06 \pm 0.17 g cm ^ { -3 } , and the planet orbits the star at a distance of 0.03894 AU .
Ephemerides for the transit centers are T _ { c } = 2 , 454 , 218.7594 \pm 0.0029 + N \times ( 2.899703 \pm 0.000054 ) ( HJD ) .