Exploring B4: A pulsating sdB star, in a binary, in the open cluster NGC 6791

Herbert Pablo, Steven D. Kawaler, Elizabeth M. Green

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


We report on Kepler photometry of the hot subdwarf B (sdB) star B4 in the open cluster NGC 6791. We confirm that B4 is a reflection effect binary with an sdB component and a low-mass main-sequence companion with a circular 0.3985 day orbit. The sdB star is a g-mode pulsator (a V1093 Her star) with periods ranging from 2384s to 7643s. Several of the pulsation modes show symmetric splitting by 0.62 μHz. Attributing this to rotational splitting, we conclude that the sdB component has a rotation period of approximately 9.63 days, indicating that tidal synchronization has not been achieved in this system. Comparison with theoretical synchronization time provides a discriminant between various theoretical models.

Original languageEnglish (US)
Article numberL47
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Oct 20 2011
Externally publishedYes


  • binaries: close
  • open clusters and associations: individual (NGC 6791)
  • stars: horizontal-branch
  • stars: oscillations

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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