We present the discovery of KELT-1b, the first transiting low-mass companion from the wide-field Kilodegree Extremely Little Telescope-North (KELT-North) transit survey. A joint analysis of the spectroscopic, radial velocity, and photometric data indicates that the V = 10.7 primary is a mildly evolved mid-F star with T-eff = 6516 +/- 49 K, log g = 4.228(-0.021)(+0.014), and [Fe/H] = 0.052 +/- 0.079, with an inferred mass M* = 1.335 +/- 0.063M(circle dot) and radius R* = 1.471(-0.035)(+0.045) R-circle dot. The companion is a low-mass brown dwarf or a super-massive planet with mass M-P = 27.38 +/- 0.93 M-Jup and radius R-P = 1.116(-0.029)(+0.038) R-Jup. The companion is on a very short (similar to 29 hr) period circular orbit, with an ephemeris T-c(BJD(TDB)) = 2455909.29280 +/- 0.00023 and P = 1.217501 +/- 0.000018 days. KELT-1b receives a large amount of stellar insolation, resulting in an estimated equilibrium temperature assuming zero albedo and perfect redistribution of T-eq = 2423(-27)(+34) K. Comparison with standard evolutionary models suggests that the radius of KELT-1b is likely to be significantly inflated. Adaptive optics imaging reveals a candidate stellar companion to KELT-1 with a separation of 588 +/- 1 mas, which is consistent with an M dwarf if it is at the same distance as the primary. Rossiter-McLaughlin measurements during transit imply a projected spin-orbit alignment angle lambda = 2 +/- 16 deg, consistent with a zero obliquity for KELT-1. Finally, the v sin I* = 56 +/- 2 km s(-1) of the primary is consistent at similar to 2 sigma with tidal synchronization. Given the extreme parameters of the KELT-1 system, we expect it to provide an important testbed for theories of the emplacement and evolution of short-period companions, as well as theories of tidal dissipation and irradiated brown dwarf atmospheres.
R. J. Siverd, T. G. Beatty, J. Pepper, J. D. Eastman, K. Collins, A. Bieryla, D. W. Latham, L. A. Buchhave, Eric L.N. Jensen, J. R. Crepp, R. Street, K. G. Stassun, B. S. Gaudi, P. Berlind, M. L. Calkins, D. L. DePoy, G. A. Esquerdo, B. J. Fulton, G. Fürész, J. C. Geary, A. Gould, L. Hebb, J. F. Kielkopf, J. L. Marshall, R. Pogge, K. Z. Stanek, R. P. Stefanik, A. H. Szentgyorgyi, M. Trueblood, P. Trueblood, A. M. Stutz, and J. L. Van Saders.
"KELT-1b: A Strongly Irradiated, Highly Inflated, Short Period, 27 Jupiter-Mass Companion Transiting A Mid-F Star".