KOI-54: The Kepler discovery of tidally excited pulsations and brightenings in a highly eccentric binary

William F. Welsh, Jerome A. Orosz, Conny Aerts, Timothy M. Brown, Erik Brugamyer, William D. Cochran, Ronald L. Gilliland, Joyce Ann Guzik, D. W. Kurtz, David W. Latham, Geoffrey W. Marcy, Samuel N. Quinn, Wolfgang Zima, Christopher Allen, Natalie M. Batalha, Steve Bryson, Lars A. Buchhave, Douglas A. Caldwell, Thomas N. Gautier, Steve B. HowellK. Kinemuchi, Khadeejah A. Ibrahim, Howard Isaacson, Jon M. Jenkins, Andrej Prsa, Martin Still, Rachel Street, Bill Wohler, David G. Koch, William J. Borucki

Research output: Contribution to journalArticle

104 Scopus citations

Abstract

Kepler observations of the star HD 187091 (KIC 8112039, hereafter KOI-54) revealed a remarkable light curve exhibiting sharp periodic brightening events every 41.8 days with a superimposed set of oscillations forming a beating pattern in phase with the brightenings. Spectroscopic observations revealed that this is a binary star with a highly eccentric orbit, e = 0.83. We are able to match the Kepler light curve and radial velocities with a nearly face-on (i = 55) binary star model in which the brightening events are caused by tidal distortion and irradiation of nearly identical A stars during their close periastron passage. The two dominant oscillations in the light curve, responsible for the beating pattern, have frequencies that are the 91st and 90th harmonic of the orbital frequency. The power spectrum of the light curve, after removing the binary star brightening component, reveals a large number of pulsations, 30 of which have a signal-to-noise ratio ≳7. Nearly all of these pulsations have frequencies that are either integer multiples of the orbital frequency or are tidally split multiples of the orbital frequency. This pattern of frequencies unambiguously establishes the pulsations as resonances between the dynamic tides at periastron and the free oscillation modes of one or both of the stars. KOI-54 is only the fourth star to show such a phenomenon and is by far the richest in terms of excited modes.

Original languageEnglish (US)
Article number4
JournalAstrophysical Journal, Supplement Series
Volume197
Issue number1
DOIs
StatePublished - Nov 1 2011

    Fingerprint

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Welsh, W. F., Orosz, J. A., Aerts, C., Brown, T. M., Brugamyer, E., Cochran, W. D., Gilliland, R. L., Guzik, J. A., Kurtz, D. W., Latham, D. W., Marcy, G. W., Quinn, S. N., Zima, W., Allen, C., Batalha, N. M., Bryson, S., Buchhave, L. A., Caldwell, D. A., Gautier, T. N., ... Borucki, W. J. (2011). KOI-54: The Kepler discovery of tidally excited pulsations and brightenings in a highly eccentric binary. Astrophysical Journal, Supplement Series, 197(1), [4]. https://doi.org/10.1088/0067-0049/197/1/4