Two warm, low-density sub-Jovian planets orbiting bright stars in K2 campaigns 13 and 14

We report the discovery of two planetstransiting the bright stars HD 89345 (EPIC 248777106, V = 9.376, K = 7.721) in K2 Campaign 14 and HD 286123 (EPIC 247098361, V = 9.822, K = 8.434) in K2 Campaign 13. Both stars are G-type stars, one of which is at or near the end of its main sequencelifetime, and the other that is just over halfway through its main sequencelifetime. HD 89345 hosts a warm sub- Saturn(0.616 $R_J$, 0.103 $M_J$, $T_{eq}$ = 1059 K) in an 11.81-day orbit. The planetis similar in size to WASP-107b, which falls in the transition region between ice giantsand gas giants. HD 286123 hosts a Jupiter-sized, low-mass planet(1.080 $R_J$, 0.408 $M_J$, $T_{eq}$ = 999 K) in an 11.17-day, mildly eccentric orbit, with $e = 0.268\pm 0.037$. Given that they orbit relatively evolved main-sequencestars with ages of ~5-7 Gyr, and have orbital periodslonger than 10 days, these planetsare interesting candidates for studies of gas planetevolution, migration, and (potentially) re-inflation. Both planetshave spent their entire lifetimes near the proposed stellar irradiation threshold at which giant planetsbecome inflated, and neither shows any sign of radius inflation. They probe the regime where inflation begins to become noticeable and are valuable in constraining planetinflation models. In addition, the brightness of the host stars, combined with large atmospheric scale heightsof the planets, makes these two systems exceptionally favorable targets for transit spectroscopy to study their atmospheres and perhaps provide insight into the physical mechanisms that that lead to inflated hot Jupiters.