KELT-1b: A strongly irradiated, highly inflated, short period, 27 jupiter-mass companion transiting a MID-F star

Robert J. Siverd, Thomas G. Beatty, Joshua Pepper, Jason D. Eastman, Karen Collins, Allyson Bieryla, David W. Latham, Lars A. Buchhave, Eric L.N. Jensen, Justin R. Crepp, Rachel Street, Keivan G. Stassun, B. Scott Gaudi, Perry Berlind, Michael L. Calkins, D. L. Depoy, Gilbert A. Esquerdo, Benjamin J. Fulton, Gábor Furész, John C. GearyAndrew Gould, Leslie Hebb, John F. Kielkopf, Jennifer L. Marshall, Richard Pogge, K. Z. Stanek, Robert P. Stefanik, Andrew H. Szentgyorgyi, Mark Trueblood, Patricia Trueblood, Amelia M. Stutz, Jennifer L. Van Saders

Research output: Contribution to journalArticlepeer-review

208 Scopus citations


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 +0.014-0.021, and [Fe/H] = 0.052 ± 0.079, with an inferred mass M* = 1.335 ± 0.063 M and radius R* = 1.471+0.045 -0.035 R. The companion is a low-mass brown dwarf or a super-massive planet with mass MP= 27.38 ± 0.93 MJup and radius RP= 1.116+0.038-0.029RJup. The companion is on a very short (∼29 hr) period circular orbit, with an ephemeris Tc(BJDTDB) = 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+34 -27 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 λ = 2 ± 16 deg, consistent with a zero obliquity for KELT-1. Finally, the vsin I* = 56 ± 2 km s-1 of the primary is consistent at ∼2σ 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.

Original languageEnglish (US)
Article number123
JournalAstrophysical Journal
Issue number2
StatePublished - Dec 10 2012
Externally publishedYes


  • planetary systems
  • stars: individual: KELT-1 TYC 2785-2130-1
  • techniques: photometric
  • techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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  • KELT-1 photometry and spectroscopy follow-up

    Siverd, R. J. (Creator), Beatty, T. (Creator), Pepper, J. (Creator), Eastman, J. D. (Creator), Collins, K. (Creator), Bieryla, A. (Creator), Latham, D. W. (Creator), Buchhave, L. A. (Creator), Jensen, E. L. N. (Contributor), Crepp, J. R. (Creator), Street, R. (Creator), Stassun, K. G. (Creator), Scott Gaudi, G. B. (Contributor), Berlind, P. (Creator), Calkins, M. L. (Creator), Depoy, D. L. (Creator), Esquerdo, G. A. (Creator), Fulton, B. J. (Creator), Furész, G. (Contributor), Geary, J. C. (Creator), Gould, A. (Creator), Hebb, L. (Creator), Kielkopf, J. F. (Creator), Marshall, J. L. (Creator), Pogge, R. (Creator), Stanek, K. Z. (Creator), Stefanik, R. P. (Creator), Szentgyorgyi, A. H. (Creator), Trueblood, M. (Creator), Trueblood, P. (Creator), Stutz, A. M. (Creator), Van Saders, J. L. (Creator), Pepper, J. (Creator), Eastman, J. D. (Creator), Collins, K. (Creator), Latham, D. W. (Creator), Jensen, E. L. N. (Contributor), Stassun, K. G. (Creator), Gaudi, B. S. (Creator), Calkins, M. L. (Creator), Gould, A. (Creator), Pogge, R. (Creator) & Stanek, K. Z. (Creator), Centre de Donnees Strasbourg (CDS), 2014


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