K2-99 revisited: a non-inflated warm Jupiter, and a temperate giant planet on a 522-d orbit around a subgiant

TL;DR

This study refines the properties of the K2-99 planetary system, revealing a non-inflated warm Jupiter and a temperate outer giant planet on a 522-day orbit around a subgiant star, using new photometric, spectroscopic, and asteroseismic data.

Contribution

The paper provides updated stellar and planetary parameters for K2-99, including the discovery of a non-inflated warm Jupiter and detailed orbital characterization of an outer giant planet.

Findings

K2-99 is smaller than previously thought, with a radius of 2.55 R_sun.

K2-99b is a non-inflated warm Jupiter with a radius of 1.06 R_Jup.

The outer planet has a minimum mass of 8.4 M_Jup, an eccentric orbit, and a period of about 522 days.

Abstract

We report new photometric and spectroscopic observations of the K2-99 planetary system. Asteroseismic analysis of the short-cadence light curve from K2's Campaign 17 allows us to refine the stellar properties. We find K2-99 to be significantly smaller than previously thought, with $R_{\star} = 2.55\pm0.02$ $\mathrm{R_\odot}$. The new light curve also contains four transits of K2-99b, which we use to improve our knowledge of the planetary properties. We find the planet to be a non-inflated warm Jupiter, with $R_\mathrm{b} = 1.06 \pm 0.01$ $\mathrm{R_{Jup}}$. Sixty new radial velocity measurements from HARPS, HARPS-N, and HIRES enable the determination of the orbital parameters of K2-99c, which were previously poorly constrained. We find that this outer planet has a minimum mass $M_\mathrm{c} \sin i_\mathrm{c} = 8.4\pm0.2$ $\mathrm{M_{Jup}}$, and an eccentric orbit ($e_\mathrm{c} = 0.210 \pm 0.009$) with a period of $522.2\pm1.4$ d. Upcoming TESS observations in 2022 have a good chance of detecting the transit of this planet, if the mutual inclination between the two planetary orbits is small.