Kepler and the Behemoth: Three Mini-Neptunes in a 40 Million Year Old Association

Abstract Stellar positions and velocities from Gaia are yielding a new view of open cluster dispersal. Here we present an analysis group stars spanning Cepheus ( l = 100°) to Hercules 40°), hereafter the Cep-Her complex. The includes four Kepler objects interest: Kepler-1643 b R p 2.32 ± 0.13 ⊕ , P 5.3 days), KOI-7368 2.22 0.12 6.8 KOI-7913 Ab 2.34 0.18 24.2 Kepler-1627 3.85 0.11 7.2 days). latter Neptune-sized planet is in part complex called δ Lyr cluster. focus on former three systems, which other regions association. Based kinematic evidence Gaia, stellar rotation periods TESS, spectroscopy, these also ≈40 million years (Myr) old. More specifically, find that 46 − 7 + 9 Myr old, based its membership dense subcluster RSG-5. ${36}_{-8}^{+10}$?> 36 8 10 diffuse region call CH-2. transit shapes high-resolution imaging, all most likely planets, with false-positive probabilities 6 × 10 −9 4 −3 1 −4 for Kepler-1643, KOI-7368, KOI-7913, respectively. These planets demonstrate mini-Neptunes sizes ≈2 Earth radii exist at ages 40 Myr.