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Article overview
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Can we predict the global magnetic topology of a pre-main sequence star from its position in the Hertzsprung-Russell diagram? | | S. G. Gregory
; J.-F. Donati
; J. Morin
; G. A. J. Hussain
; N. J. Mayne
; L. A. Hillenbrand
; M. Jardine
; | | Date: |
22 Jun 2012 | | Abstract: | ZDI studies have shown that the magnetic fields of T Tauri stars can be
significantly more complex than a simple dipole and can vary markedly between
sources. We collect and summarize the magnetic field topology information
obtained to date and present Hertzsprung-Russell (HR) diagrams for the stars in
the sample. Intriguingly, the large scale field topology of a given pre-main
sequence (PMS) star is strongly dependent upon the stellar internal structure,
with the strength of the dipole component of its multipolar magnetic field
decaying rapidly with the development of a radiative core. Using the
observational data as a basis, we argue that the general characteristics of the
global magnetic field of a PMS star can be determined from its position in the
HR diagram. Moving from hotter and more luminous to cooler and less luminous
stars across the PMS of the HR diagram, we present evidence for four distinct
magnetic topology regimes. Stars with large radiative cores, empirically
estimated to be those with a core mass in excess of ~40 per cent of the stellar
mass, host highly complex and dominantly non-axisymmetric magnetic fields,
while those with smaller radiative cores host axisymmetric fields with field
modes of higher order than the dipole dominant (typically, but not always, the
octupole). Fully convective stars stars above ~0.5 MSun appear to host
dominantly axisymmetric fields with strong (kilo-Gauss) dipole components.
Based on similarities between the magnetic properties of PMS stars and main
sequence M-dwarfs with similar internal structures, we speculate that a
bistable dynamo process operates for lower mass stars (<~0.5 MSun at an age of
a few Myr) and that they will be found to host a variety of magnetic field
topologies. If the magnetic topology trends across the HR diagram are confirmed
they may provide a new method of constraining PMS stellar evolution models. | | Source: | arXiv, 1206.5238 | | Services: | Forum | Review | PDF | Favorites | |
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