KELT-16b: A Highly Irradiated, Ultra-short Period Hot Jupiter Nearing Tidal Disruption

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, log g⋆ = 4.253^(+0.031)_(-0.036), [Fe/H] = -0.002^(+0.086)_(-0.085), M⋆ = 1.211^(+0.043)_(-0.046) M⊙, and R⋆ = 1.360^(+0.064)_(-0.15)R⊙. The planet is a relatively high-mass inflated gas giant with M_P = 2.75^(+0.16)_(-0.15)M_J, R_P = 1.415^(+0.084)_(-0.067)R_J, density Ρ_p = 1.20 ± 0.18 g cm^(−3), surface gravity Log g_P = 3.530^(+0.042)_(-0.049), and T_(eq) = 2453^(+55)_(-47)K. The best-fitting linear ephemeris is T_C = 2457247.24791 ± 0.00019 BJD_(TBD) 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 ×105 years (for a stellar tidal quality factor of Q’* = 10^5). 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.