HATS-15b and HATS-16b: two massive planets transiting old G dwarf stars

Abstract

We report the discovery of HATS-15 b and HATS-16 b, two massive transiting extrasolar planets orbiting evolved (∼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 ± 0.15 MJ and radius of 1.105 ± 0.040 RJ, and it completes its orbit in about 1.7 days. HATS-16 b is a very massive hot Jupiter with mass of 3.27 ± 0.19 MJ and radius of 1.30 ± 0.15 RJ; it orbits around its G3 V parent star (V = 13.8 mag) in ∼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.