S. G. Gregory, J. -F. Donati
Traditionally models of accretion of gas on to T Tauri stars have assumed a
dipole stellar magnetosphere, partly for simplicity, but also due to the lack
of information about their true magnetic field topologies. Before and since the
first magnetic maps of an accreting T Tauri star were published in 2007 a new
generation of magnetospheric accretion models have been developed that
incorporate multipole magnetic fields. Three-dimensional models of the
large-scale stellar magnetosphere with an observed degree of complexity have
been produced via numerical field extrapolation from observationally derived T
Tauri magnetic maps. Likewise, analytic and magnetohydrodynamic models with
multipolar stellar magnetic fields have been produced. In this conference
review article we compare and contrast the numerical field extrapolation and
analytic approaches, and argue that the large-scale magnetospheres of some (but
not all) accreting T Tauri stars can be well described by tilted dipole plus
tilted octupole field components. We further argue that the longitudinal field
curve, whether derived from accretion related emission lines, or from
photospheric absorption lines, provides poor constrains on the large-scale
magnetic field topology and that detailed modeling of the rotationally
modulated Stokes V signal is required to recover the true field complexity. We
conclude by examining the advantages, disadvantages and limitations of both the
field extrapolation and analytic approaches, and also those of
magnetohydrodynamic models.
View original:
http://arxiv.org/abs/1110.5901
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