KELT-16b: A highly irradiated, ultra-short period hot Jupiter nearing tidal disruption

Abstract

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. A global analysis of the system shows KELT-16 to be an F7V star with $T_{\text{eff}}=6236\pm 54$ K, $\log g_{\star }=4.253_{-0.036}^{+0.031}$, [Fe/H] = -0.002${}_{-0.085}^{+0.086}$, $M_{\star }=1.211_{-0.046}^{+0.043}{M}_{\odot }$, and $R_{\star }=1.360_{-0.053}^{+0.064}{R}_{\odot }$. The planet is a relatively high mass inflated gas giant with $M_{\text{P}}=2.75_{-0.15}^{+0.16}{M}_{\text{J}}$, $R_{\text{P}}=1.415_{-0.067}^{+0.084}{R}_{\text{J}}$, density $\ddot{I}{}_{\text{P}}=1.20\pm 0.18$ g cm${}^{-3}$, surface gravity $\log g_{\text{P}}=3.530_{-0.049}^{+0.042}$, and $T_{\text{eq}}=2453_{-47}^{+55}$ K. The best-fitting linear ephemeris is $T_{\text{C}}=2457247.24791\pm 0.00019$ BJD${}_{tdb}$ and $P=0.9689951\pm 0.0000024$ d. 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 HST, Spitzer, and eventually JWST. 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 $\sim$ 1.7 Roche radii from its host star, and could be tidally disrupted in as little as a few $\times 10^5$ years (for a stellar tidal quality factor of $Q_{\ast }^{\prime }=10^5$). Finally, the likely existence of a widely separated bound stellar companion in the KELT-16 system makes it possible that Kozai-Lidov oscillations played a role in driving KELT-16b inward to its current precarious orbit.

16 pages, 18 Figures, 7 Tables, Accepted for publication in AJ