K2-98 b: A 32-M${}_{\oplus }$ Neptune-sized planet in a 10-day orbit transiting an F8 star

Abstract

We report the discovery of K2-98 b (EPIC 211391664 b), a transiting Neptune-sized planet monitored by the K2 mission during its campaign 5. We combine the K2 time-series data with ground-based photometric and spectroscopic follow-up observations to confirm the planetary nature of the object and derive its mass, radius, and orbital parameters. K2-98 b is a warm Neptune-like planet in a 10-day orbit around a V=12.2~mag F-type star with $M_{\star }$=$1.074\pm 0.042$, $R_{\star }$=$1.311_{-0.048}^{+0.083}$, and age of $5.2_{-1.0}^{+1.2}$~Gyr. We derive a planetary mass and radius of $M_{\mathrm{p}}$=$32.2\pm 8.1$ and $R_{\mathrm{p}}$=$4.3_{-0.2}^{+0.3}$. K2-98 b joins the relatively small group of Neptune-sized planets whose both mass and radius have been derived with a precision better than 25 %. We estimate that the planet will be engulfed by its host star in $\sim$3~Gyr, due to the evolution of the latter towards the red giant branch.

11 pages, 4 figures, Accepted for publication in AJ