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

TL;DR

This paper reports the discovery of a transiting warm Jupiter orbiting a subgiant star in an eccentric orbit, with evidence suggesting a long-period third companion, likely a brown dwarf.

Contribution

It presents the first detection of a transiting warm Jupiter around a subgiant star with an eccentric orbit and evidence for an additional long-period companion.

Findings

Discovery of a transiting warm Jupiter with an 18.25-day eccentric orbit.

Confirmation of the planetary nature via radial velocities.

Evidence for a third body, possibly a brown dwarf, in the system.

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 $1.60^{+0.14}_{-0.10}~M_\odot$ 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.