skip to main content

SciTech ConnectSciTech Connect

Title: DYNAMO ACTION AND MAGNETIC CYCLES IN F-TYPE STARS

Magnetic activity and differential rotation are commonly observed features on main-sequence F-type stars. We seek to make contact with such observations and to provide a self-consistent picture of how differential rotation and magnetic fields arise in the interiors of these stars. The three-dimensional magnetohydrodynamic anelastic spherical harmonic code is employed to simulate global-scale convection and dynamo processes in a 1.2 M{sub ☉} F-type star at two rotation rates. The simulations are carried out in spherical shells that encompass most of the convection zone and a portion of the stably stratified radiative zone below it, allowing us to explore the effects a stable zone has upon the morphology of the global-scale magnetic fields. We find that dynamo action with a high degree of time variation occurs in the star rotating more rapidly at 20 Ω{sub ☉}, with the polarity of the mean field reversing on a timescale of about 1600 days. Between reversals, the magnetic energy rises and falls with a fairly regular period, with three magnetic energy cycles required to complete a reversal. The magnetic energy cycles and polarity reversals arise due to a linking of the polar-slip instability in the stable region and dynamo action present in the convectionmore » zone. For the more slowly rotating case (10 Ω{sub ☉}), persistent wreaths of magnetism are established and maintained by dynamo action. Compared to their hydrodynamic progenitors, the dynamo states here involve a marked reduction in the exhibited latitudinal differential rotation, which also vary during the course of a cycle.« less
Authors:
;  [1] ;  [2]
  1. JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309 (United States)
  2. DSM/IRFU/SAp, UMR AIM, Paris-Saclay CEA Saclay, F-91191 Gif-sur-Yvette Cedex (France)
Publication Date:
OSTI Identifier:
22270574
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 777; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; CONVECTION; MAGNETIC FIELDS; MAGNETISM; MAGNETOHYDRODYNAMICS; MAIN SEQUENCE STARS; MEAN-FIELD THEORY; ROTATION; SPHERICAL CONFIGURATION; THREE-DIMENSIONAL CALCULATIONS; TURBULENCE; ZONES