MELANGE-3: A mini-Pleiades harboring two transiting planets in the Kepler field

We describe a young association (MELANGE-3) in the Kepler field harboring two transiting planetary systems (KOI-3876 and Kepler-970). We initially identified MELANGE-3 by searching for kinematic and spatial overdensities around stars with high levels of lithium (in this case, KOI-3876). To better determine the age and membership of MELANGE-3, we combine archival light curves, velocities, and astrometry, with new high-resolution spectra of stars nearest KOI-3876 spatially and kinematically. The resulting rotation sequence, lithium levels, and color-magnitude diagram of members are all consistent with the Pleiades, confirming the population is co-eval and providing an age estimate of 105±10 Myr. MELANGE-3 may be one edge of the recently identified Theia 316 stream, also estimated to be ~108 Myr. For the two exoplanet systems, we revise the stellar and planetary parameters, taking into account the newly-determined age. We fit the 4.5 yr Kepler light curves and find that KOI-3876.01 is a 2.0 ±0.1R⊕ planet that orbits its star every 19.58 days, while Kepler-970 is a 2.8±0.2R⊕ planet that orbits its star every 16.73 days. KOI-3876 was previously flagged as an eclipsing binary, but we rule this out using radial velocities from APOGEE and statistically validate the signal as planetary in origin. Given its overlap with the Kepler field, MELANGE-3 is valuable for studies of spot evolution on timescales of years, and both planets contribute to the growing work on transiting planets in young stellar associations.Bachelor of Scienc