HATS-9b and HATS-10b: Two Compact Hot Jupiters in Field 7 of the K2 Mission

Abstract: We report the discovery of two transiting extrasolar planets by the HATSouth survey. HATS-9b orbits an old (10.8 $\pm$ 1.5 Gyr) V=13.3 G dwarf star, with a period P = 1.9153 d. The host star has a mass of 1.03 M${\odot}$, radius of 1.503 R$\odot$ and effective temperature 5366 $\pm$ 70 K. The planetary companion has a mass of 0.837 M$J$, and radius of 1.065 R$_J$ yielding a mean density of 0.85 g cm$^{-3}$. HATS-10b orbits a V=13.1 G dwarf star, with a period P = 3.3128 d. The host star has a mass of 1.1 M$\odot$, radius of 1.11 R$_\odot$ and effective temperature 5880 $\pm$ 120 K. The planetary companion has a mass of 0.53 M$_J$, and radius of 0.97 R$_J$ yielding a mean density of 0.7 g cm$^{-3}$. Both planets are compact in comparison with planets receiving similar irradiation from their host stars, and lie in the nominal coordinates of Field 7 of K2 but only HATS-9b falls on working silicon. Future characterisation of HATS-9b with the exquisite photometric precision of the Kepler telescope may provide measurements of its reflected light signature.