K2-99: a subgiant hosting a transiting warm Jupiter in an eccentric orbit and a long-period companion

Abstract

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 $1.60_{-0.10}^{+0.14}{M}_{\odot }$ and radius $3.1\pm 0.1R_{\odot }$. The planet has a mass of $0.97\pm 0.09M_{\mathrm{Jup}}$ and a radius $1.29\pm 0.05R_{\mathrm{Jup}}$. A measured systemic radial acceleration of $-2.12\pm 0.04\mathrm{m}{\mathrm{s}}^{-1}{\mathrm{d}}^{-1}$ 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.

10 pages, 6 figures, 4 tables, accepted for publication in MNRAS