We report the discovery of HAT-P-15b , a transiting extrasolar planet in the ‘ period valley ’ , a relatively sparsely-populated period regime of the known extrasolar planets .
The host star , GSC 2883-01687 , is a G5 dwarf with V = 12.16 .
It has a mass of 1.01 \pm 0.04 M _ { \sun } , radius of 1.08 \pm 0.04 R _ { \sun } , effective temperature 5568 \pm 90 K , and metallicity [ Fe / H ] = +0.22 \pm 0.08 .
The planetary companion orbits the star with a period P = 10.863502 \pm 0.000027 d , transit epoch T _ { c } = 2454638.56019 \pm 0.00048 ( BJD ) , and transit duration 0.2285 \pm 0.0015 d. It has a mass of 1.946 \pm 0.066 M _ { J } , and radius of 1.072 \pm 0.043 R _ { J } yielding a mean density of 1.96 \pm 0.22 g cm ^ { -3 } .
At an age of 6.8 _ { -1.6 } ^ { +2.5 } Gyr , the planet is H/He-dominated and theoretical models require about 2 % ( 10 M _ { \earth } ) worth of heavy elements to reproduce its measured radius .
With an estimated equilibrium temperature of \sim 820 K during transit , and \sim 1000 K at occultation , HAT-P-15b is a potential candidate to study moderately cool planetary atmospheres by transmission and occultation spectroscopy .