The Curious Case of KOI 4: Confirming Kepler's First Exoplanet Detection

Ashley Chontos*, Daniel Huber, David W. Latham, Allyson Bieryla, Vincent Van Eylen, Timothy R. Bedding, Travis Berger, Lars A. Buchhave, Tiago L. Campante, William J. Chaplin, Isabel L. Colman, Jeff L. Coughlin, Guy Davies, Feruyuki Hirano, Andrew W. Howard, Howard Isaacson

*Corresponding author for this work

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The discovery of thousands of planetary systems by Kepler has demonstrated that planets are ubiquitous. However, a major challenge has been the confirmation of Kepler planet candidates, many of which still await confirmation. One of the most enigmatic examples is KOI 4.01, Kepler's first discovered planet candidate detection (as KOI 1.01, 2.01, and 3.01 were known prior to launch). Here we present the confirmation and characterization of KOI 4.01 (now Kepler-1658), using a combination of asteroseismology and radial velocities. Kepler-1658 is a massive, evolved subgiant (M star = 1.45 ± 0.06 M ⊙, R star = 2.89 ± 0.12 R ⊙) hosting a massive Mp = 5.88 ± 0.47 Ms, Rp =1.07±0.05 RJ) hot Jupiter that orbits every 3.85 days. Kepler-1658 joins a small population of evolved hosts with short-period (≤100 days) planets and is now the closest known planet in terms of orbital period to an evolved star. Because of its uniqueness and short orbital period, Kepler-1658 is a new benchmark system for testing tidal dissipation and hot Jupiter formation theories. Using all four years of the Kepler data, we constrain the orbital decay rate to be P ≤ −0.42 s yr−1, corresponding to a strong observational limit of Q' star ≥ 4.826 × 103 for the tidal quality factor in evolved stars. With an effective temperature of Teff ~ 6200 K, Kepler-1658 sits close to the spin–orbit misalignment boundary at ~6250 K, making it a prime target for follow-up observations to better constrain its obliquity and to provide insight into theories for hot Jupiter formation and migration.
Original languageEnglish
Article number192
JournalAstrophysical Journal
Issue number5
Number of pages14
Publication statusPublished - 2019


  • Asteroseismology
  • Planets and satellites: individual (KOI 4.01)
  • Stars: individual (Kepler-1658)
  • Techniques: photometric, radial velocities, spectroscopic


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