A further "degree of freedom" in the rotational evolution of stars

V Holzwarth, Moira Mary Jardine

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)

Abstract

Observational and theoretical investigations provide evidence for non-uniform spot and magnetic flux distributions on rapidly rotating stars, which have a significant impact on their angular momentum loss rate through magnetised winds. Supplementing the formalism of MacGregor & Brenner ( 1991) with a latitude-dependent magnetised wind model, we analyse the e. ect of analytically prescribed surface distributions of open magnetic flux with different shapes and degrees of non-uniformity on the rotational evolution of a solar-like star. The angular momentum redistribution inside the star is treated in a qualitative way, assuming an angular momentum transfer between the rigidly-rotating radiative and convective zones on a constant coupling timescale of 15 Myr; for the sake of simplicity we disregard interactions with circumstellar disks. We find that non-uniform flux distributions entail rotational histories which differs significantly from those of classical approaches, with differences cumulating up to 200% during the main sequence phase. Their impact is able to mimic deviations of the dynamo efficiency from linearity of up to 40% and nominal dynamo saturation limits at about 35 times the solar rotation rate. Concentrations of open magnetic flux at high latitudes thus assist in the formation of very rapidly rotating stars in young open clusters, and ease the necessity for a dynamo saturation at small rotation rates. However, since our results show that even minor amounts of open flux at intermediate latitudes, as observed with Zeeman-Doppler imaging techniques, are sufficient to moderate this reduction of the AM loss rate, we suggest that non-uniform flux distributions are a complementary rather than an alternative explanation for very rapid stellar rotation.

Original languageEnglish
Pages (from-to)661-671
Number of pages11
JournalAstronomy & Astrophysics
Volume444
DOIs
Publication statusPublished - Dec 2005

Keywords

  • stars : rotation
  • stars : winds, outflows
  • stars : magnetic fields
  • stars : mass-loss
  • stars : evolution magnetohydrodynamics (MHD)
  • SOLAR-TYPE STARS
  • LOW-MASS STARS
  • ANGULAR-MOMENTUM EVOLUTION
  • MAIN-SEQUENCE STARS
  • YOUNG OPEN CLUSTERS
  • X-RAY-EMISSION
  • AB-DORADUS
  • MAGNETIC BRAKING
  • STELLAR WINDS
  • ACTIVE STARS

Fingerprint

Dive into the research topics of 'A further "degree of freedom" in the rotational evolution of stars'. Together they form a unique fingerprint.

Cite this