KELT-2Ab: A hot jupiter transiting the bright (V = 8.77) primary star of a binary system

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

Research output: Contribution to journalArticlepeer-review

40 Scopus citations


We report the discovery of KELT-2Ab, a hot Jupiter transiting the bright (V = 8.77) primary star of the HD42176 binary system. The host is a slightly evolved late F-star likely in the very short-lived "blue-hook" stage of evolution, with T eff = 6148 ± 48 K, log g = 4.030 +0.015 - 0.026 and [Fe/H] = 0.034 ± 0.78. The inferred stellar mass is M * = 1.314+0.063 - 0.060 M and the star has a relatively large radius of R * = 1.836+0.066 - 0.046 R . The planet is a typical hot Jupiter with period 4.1137913 ± 0.00001 days and a mass of MP = 1.524 ± 0.088 M J and radius of RP = 1.290+0.064 - 0.050 R J. This is mildly inflated as compared to models of irradiated giant planets at the 4Gyr age of the system. KELT-2A is the third brightest star with a transiting planet identified by ground-based transit surveys, and the ninth brightest star overall with a transiting planet. KELT-2Ab's mass and radius are unique among the subset of planets with V < 9 host stars, and therefore increases the diversity of bright benchmark systems. We also measure the relative motion of KELT-2A and -2B over a baseline of 38years, robustly demonstrating for the first time that the stars are bound. This allows us to infer that KELT-2B is an early K dwarf. We hypothesize that through the eccentric Kozai mechanism KELT-2B may have emplaced KELT-2Ab in its current orbit. This scenario is potentially testable with Rossiter-McLaughlin measurements, which should have an amplitude of 44m s-1.

Original languageEnglish (US)
Article numberL39
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Sep 10 2012

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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