We report the discovery from K2 of a transiting planet in an 18.25-d, eccentric (0.19$\pm$ 0.04) orbit around K2-99, an 11th magnitude subgiant in Virgo. We confirm the planetary nature of the companion with radial velocities, and determine that the star is a metal-rich ([Fe/H] = 0.20$\pm$0.05) subgiant, with mass $1.60^{ +0.14}_{ -0.10}~M_\odot$ and radius $3.1\pm 0.1~R_\odot$. The planet has a mass of $0.97\pm0.09~M_{ \rm Jup}$ and a radius $1.29\pm0.05~R_{ \rm Jup}$. A measured systemic radial acceleration of $-2.12\pm0.04~{ \rm m s^{ -1} d^{ -1}}$ offers compelling evidence for the existence of a third body in the system, perhaps a brown dwarf orbiting with a period of several hundred days.
Categories: astro-ph.EP