2019ApJS..240...13L

We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South survey. KELT-22Ab transits the moderately bright (V ∼ 11.1) Sun-like G2V star TYC 7518-468-1. The planet has an orbital period of P=1.3866529±0.0000027 days, a radius of R_P=1.285_–0.071^+0.12R_J, and a relatively large mass of M_P=3.47_–0.14^+0.15M_J. The star has R_*=1.099_–0.046^+0.079R_☉, M_*=1.092_–0.041^+0.045M_☉, T_eff=5767_–49⁺⁵⁰ K, logg_*=4.393_–0.060^+0.039 (cgs), and [m/H] = +0.259_–0.083^+0.085; thus other than its slightly super-solar metallicity, it appears to be a near-solar twin. Surprisingly, KELT-22A exhibits kinematics and a Galactic orbit that are somewhat atypical for thin-disk stars. Nevertheless, the star is rotating rapidly for its estimated age, and shows evidence of chromospheric activity. Imaging reveals a slightly fainter companion to KELT-22A that is likely bound, with a projected separation of 6'' (∼1400 au). In addition to the orbital motion caused by the transiting planet, we detect a possible linear trend in the radial velocity of KELT-22A, suggesting the presence of another relatively nearby body that is perhaps non-stellar. KELT-22Ab is highly irradiated (as a consequence of the small semimajor axis of a/R_*=4.97), and is mildly inflated. At such small separations, tidal forces become significant. The configuration of this system is optimal for measuring the rate of tidal dissipation within the host star. Our models predict that, due to tidal forces, the semimajor axis is decreasing rapidly, and KELT-22Ab is predicted to spiral into the star within the next Gyr.