Kepler-730: A Hot Jupiter System with a Close-in, Transiting, Earth-sized Planet

Kepler-730 is a planetary system hosting a statistically validated hot Jupiter in a 6.49 day orbit and an additional transiting candidate in a 2.85 day orbit. We use spectroscopic radial velocities from the APOGEE-2N instrument, Robo-AO contrast curves, and Gaia distance estimates to statistically validate the planetary nature of the additional Earth-sized candidate. We perform astrophysical false positive probability calculations for the candidate using the available Kepler data and bolster the statistical validation using radial velocity data to exclude a family of possible binary star solutions. Using a radius estimate for the primary star derived from stellar models, we compute radii of ${1.100}_{-0.050}^{+0.047}\,{R}_{\mathrm{Jup}}$ and $0.140\pm 0.012\,{R}_{\mathrm{Jup}}$ ($1.57\pm 0.13\,{R}_{\oplus }$) for Kepler-730b and Kepler-730c, respectively. Kepler-730 is only the second compact system hosting a hot Jupiter with an inner, transiting planet.