2017AJ....153...97O

We announce the discovery of KELT-16b, a highly irradiated, ultra-short period hot Jupiter transiting the relatively bright (V = 11.7) star TYC 2688-1839-1/KELT-16. A global analysis of the system shows KELT-16 to be an F7V star with T_eff=6236±54 K, logg_*=4.253_–0.036^+0.031, [Fe/H]=-0.002_–0.085^+0.086, M_*=1.211_–0.046^+0.043 M_☉, and R_* =1.360_–0.053^+0.064R_☉. The planet is a relatively high-mass inflated gas giant with M_P=2.75_–0.15^+0.16M_J, R_P=1.415_–0.067^+0.084R_J, density ρ_P=1.20±0.18 g cm^–3, surface gravity log g_P=3.530_–0.049^+0.042, and T_eq=2453_–47⁺⁵⁵ K. The best-fitting linear ephemeris is T_C=2457247.24791±0.00019BJD_TDB and P=0.9689951±0.0000024 day. KELT-16b joins WASP-18b, -19b, -43b, -103b, and HATS-18b as the only giant transiting planets with P < 1 day. Its ultra-short period and high irradiation make it a benchmark target for atmospheric studies by the Hubble Space Telescope, Spitzer, and eventually the James Webb Space Telescope. For example, as a hotter, higher-mass analog of WASP-43b, KELT-16b may feature an atmospheric temperature-pressure inversion and day-to-night temperature swing extreme enough for TiO to rain out at the terminator. KELT-16b could also join WASP-43b in extending tests of the observed mass-metallicity relation of the solar system gas giants to higher masses. KELT-16b currently orbits at a mere ∼1.7 Roche radii from its host star, and could be tidally disrupted in as little as a few x10⁵ years (for a stellar tidal quality factor of Q_*^′⁼¹⁰5^). Finally, the likely existence of a widely separated bound stellar companion in the KELT-16 system makes it possible that Kozai-Lidov (KL) oscillations played a role in driving KELT-16b inward to its current precarious orbit.