Spin-orbit alignment for the circumbinary planet host Kepler-16 A

Joshua N. Winn, Simon Albrecht, John Asher Johnson, Guillermo Torres, William D. Cochran, Geoffrey W. Marcy, Andrew W. Howard, Howard Isaacson, Debra Fischer, Laurance Doyle, William Welsh, Joshua A. Carter, Daniel C. Fabrycky, Darin Ragozzine, Samuel N. Quinn, Avi Shporer, Steve B. Howell, David W. Latham, Jerome Orosz, Andrej PrsaRobert W. Slawson, William J. Borucki, David Koch, Thomas Barclay, Alan P. Boss, Jørgen Christensen-Dalsgaard, Forrest R. Girouard, Jon Jenkins, Todd C. Klaus, Søren Meibom, Robert L. Morris, Dimitar Sasselov, Martin Still, Jeffrey Van Cleve

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


Kepler-16 is an eccentric low-mass eclipsing binary with a circumbinary transiting planet. Here, we investigate the angular momentum of the primary star, based on Kepler photometry and Keck spectroscopy. The primary star's rotation period is 35.1 1.0 days, and its projected obliquity with respect to the stellar binary orbit is 16 24. Therefore, the three largest sources of angular momentum - the stellar orbit, the planetary orbit, and the primary's rotation - are all closely aligned. This finding supports a formation scenario involving accretion from a single disk. Alternatively, tides may have realigned the stars despite their relatively wide separation (0.2 AU), a hypothesis that is supported by the agreement between the measured rotation period and the "pseudosynchronous" period of tidal evolution theory. The rotation period, chromospheric activity level, and fractional light variations suggest a main-sequence age of 2-4Gyr. Evolutionary models of low-mass stars can match the observed masses and radii of the primary and secondary stars to within about 3%.

Original languageEnglish (US)
Article numberL1
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Nov 1 2011
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • binaries: general
  • planets and satellites: formation
  • stars: individual (Kepler-16 A, KIC 12644769)
  • stars: low-mass
  • stars: rotation


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