Doppler measurements from Subaru and Keck have revealed radial velocity variations in the V = 8.15 , G0IV star HD 149026 consistent with a Saturn-mass planet in a 2.8766 day orbit .
Photometric observations at Fairborn Observatory have detected three complete transit events with depths of 0.003 mag at the predicted times of conjunction .
HD 149026 is now the second brightest star with a transiting extrasolar planet .
The mass of the star , based on interpolation of stellar evolutionary models , is 1.3 \pm 0.1 M _ { \odot } ; together with the Doppler amplitude , K _ { 1 } = 43.3 m s ^ { -1 } , we derive a planet mass , M \sin i~ { } = 0.36 M _ { Jup } , and orbital radius of 0.042 AU .
HD 149026 is chromospherically inactive and metal-rich with spectroscopically derived [ Fe/H ] = +0.36 , T _ { eff } = 6147 K , \log g = 4.26 and v \sin i~ { } = 6.0 km s ^ { -1 } .
Based on T _ { eff } and the stellar luminosity of 2.72 L _ { \odot } , we derive a stellar radius of 1.45 R _ { \odot } .
Modeling of the three photometric transits provides an orbital inclination of 85.3 \pm 1.0 degrees and ( including the uncertainty in the stellar radius ) a planet radius of 0.725 \pm 0.05 R _ { Jup } .
Models for this planet mass and radius suggest the presence of a \sim 67 M _ { \oplus } core composed of elements heavier than hydrogen and helium .
This substantial planet core would be difficult to construct by gravitational instability .