EPIC 247418783$b$: A rocky super-Earth in a 2.2 day orbit

EPIC 247418783 is a solar-type star with a radius of R ∗ = 0 . 899 ± 0 . 034 R (cid:12) and mass of M ∗ = 0.934 ± 0.038 M (cid:12) . From K2 C13 data, we found one super-Earth planet (R p = 1 . 589 +0 . 095 − 0 . 072 R ⊕ ) transiting this star on a short period orbit (P = 2 . 225177 +6 . 6 e − 5 − 6 . 8 e − 5 days). We followed this system up with adaptive-optic imaging and spectroscopy to derive stellar parameters, search for stellar companions, and determine a planet mass. From our 75 radial velocity measurements using HIRES on Keck I and HARPS-N on Telescopio Nazionale Galileo, we constrained the mass of EPIC 247418783 b to M p = 6 . 49 ± 1 . 16 M ⊕ . We found it necessary to model correlated stellar activity radial velocity signals with a Gaussian process in order to more accurately model the effect of stellar noise on our data; the addition of the Gaussian process also improved the precision of this mass measurement. With a bulk density of ρ = 8.84 +2 . 50 − 2 . 03 g cm − 3 , the planet is consistent with an Earth-like rock/iron composition and no substantial gaseous envelope. Such an envelope, if it existed in the past, was likely eroded away by photo-evaporation during the first billion years of the star’s lifetime.