We report the discovery of HATS-15 b and HATS-16 b , two massive transiting extrasolar planets orbiting evolved ( \sim 10 Gyr ) main-sequence stars .
The planet HATS-15 b , which is hosted by a G9 V star ( V = 14.8 mag ) , is a hot Jupiter with mass of 2.17 \pm 0.15 M _ { \mathrm { J } } and radius of 1.105 \pm 0.0.040 R _ { \mathrm { J } } , and completes its orbit in nearly 1.7 days .
HATS-16 b is a very massive hot Jupiter with mass of 3.27 \pm 0.19 M _ { \mathrm { J } } and radius of 1.30 \pm 0.15 R _ { \mathrm { J } } ; it orbits around its G3 V parent star ( V = 13.8 mag ) in \sim 2.7 days .
HATS-16 is slightly active and shows a periodic photometric modulation , implying a rotational period of 12 days which is unexpectedly short given its isochronal age .
This fast rotation might be the result of the tidal interaction between the star and its planet .