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

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 $R_{\star }=2.55\pm 0.02$ ${\mathrm{R}}_{\odot }$. 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 $R_{\mathrm{b}}=1.06\pm 0.01$ ${\mathrm{R}}_{\mathrm{Jup}}$. 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 $M_{\mathrm{c}}\sin i_{\mathrm{c}}=8.4\pm 0.2$ ${\mathrm{M}}_{\mathrm{Jup}}$, and an eccentric orbit ($e_{\mathrm{c}}=0.210\pm 0.009$) with a period of $522.2\pm 1.4$ 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.

16 pages, 8 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Society