KELT-1b: A STRONGLY IRRADIATED, HIGHLY INFLATED, SHORT PERIOD, 27 JUPITER-MASS COMPANION TRANSITING A MID-F STAR

Abstract

We present the discovery of KELT-1b, the first transiting low-mass companion\nfrom the wide-field Kilodegree Extremely Little Telescope-North (KELT-North)\nsurvey. The V=10.7 primary is a mildly evolved, solar-metallicity, mid-F star.\nThe companion is a low-mass brown dwarf or super-massive planet with mass of\n27.23+/-0.50 MJ and radius of 1.110+0.037-0.024 RJ, on a very short period\n(P=1.21750007) circular orbit. KELT-1b receives a large amount of stellar\ninsolation, with an equilibrium temperature assuming zero albedo and perfect\nredistribution of 2422 K. Upper limits on the secondary eclipse depth indicate\nthat either the companion must have a non-zero albedo, or it must experience\nsome energy redistribution. Comparison with standard evolutionary models for\nbrown dwarfs suggests that the radius of KELT-1b is significantly inflated.\nAdaptive optics imaging reveals a candidate stellar companion to KELT-1, which\nis consistent with an M dwarf if bound. The projected spin-orbit alignment\nangle is consistent with zero stellar obliquity, and the vsini of the primary\nis consistent with tidal synchronization. Given the extreme parameters of the\nKELT-1 system, we expect it to provide an important testbed for theories of the\nemplacement and evolution of short-period companions, and theories of tidal\ndissipation and irradiated brown dwarf atmospheres.\n