HATS9-b and HATS10-b: Two compact hot jupiters in field 7 of the K2 mission

We report the discovery of two transiting extrasolar planets by the HATSouth survey. HATS-9b orbits an old (10.8 ± 1.5 Gyr) V = 13.3 G dwarf star with a period $P\approx 1.9153$ days. The host star has a mass of 1.03 $M_{\odot }$, radius of 1.503 $R_{\odot }$ , and effective temperature 5366 ± 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 $P\approx 3.3128$ days. The host star has a mass of 1.1 $M_{\odot }$, radius of 1.11 $R_{\odot }$ , and effective temperature 5880 ± 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 characterization of HATS-9b with the exquisite photometric precision of the Kepler telescope may provide measurements of its reflected light signature.