Cycle period, differential rotation, and meridional flow for early M dwarf stars

M. Küker, G. Rüdiger, K. Olah, K. G. Strassmeier

Research output: Contribution to journalArticle

2 Citations (Scopus)


Recent observations suggest the existence of two characteristic cycle times for early-type M stars dependent on the rotation period. They are of order one year for fast rotators (P rot < 1 day) and of order four years for slower rotators. Additionally, the equator-to-pole differences of the rotation rates with δΩ up to 0.03 rad d -1 are known from Kepler data for the fast-rotating stars. These values are well-reproduced by the theory of large-scale flows in rotating convection zones on the basis of the Λ effect. The resulting amplitudes u m of the bottom value of the meridional circulation allows for the calculation of the travel time from pole to equator at the base of the convection zone of early-type M stars. These travel times strongly increase with rotation period and they always exceed the observed cycle periods. Therefore, the operation of an advection-dominated dynamo in early M dwarfs, where the travel time must always be shorter than the cycle period, is not confirmed by our model nor the data.

Original languageEnglish
Article numberA40
JournalAstronomy and Astrophysics
Publication statusPublished - Feb 1 2019


  • Magnetohydrodynamics (MHD)
  • Stars: activity
  • Stars: late-type
  • Stars: magnetic field
  • Turbulence

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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