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The multipolar magnetic fields of accreting pre-main-sequence stars: B at the inner disk, B along the accretion flow, and B at the accretion shock | | Scott G. Gregory
; Jean-François Donati
; Gaitee A. J. Hussain
; | | Date: |
1 Sep 2016 | | Abstract: | Zeeman-Doppler imaging studies have revealed the complexity of the
large-scale magnetic fields of accreting pre-main-sequence stars. All have
multipolar magnetic fields with the octupole component being the dominant field
mode for many of the stars studied thusfar. Young accreting stars with fully
convective interiors often feature simple axisymmetric magnetic fields with
dipole components of order a kilo-Gauss (at least those of mass
$gtrsim0.5,{
m M}_odot$), while those with substantially radiative
interiors host more complex non-axisymmetric magnetic fields with dipole
components of order a few 0.1 kilo-Gauss. Here, via several simple examples, we
demonstrate that i). in most cases, the dipole component alone can be used to
estimate the disk truncation radius (but little else); ii) due the presence of
higher order magnetic field components, the field strength in the accretion
spots is far in excess of that expected if a pure dipole magnetic field is
assumed. (Fields of $sim$6$,{
m kG}$ have been measured in accretion
spots.); iii) if such high field strengths are taken to be representative of
the polar strength of a dipole magnetic field, the disk truncation radius would
be overestimated. The effects of multipolar magnetic fields must be considered
in both models of accretion flow and of accretion shocks. | | Source: | arXiv, 1609.0273 | | Services: | Forum | Review | PDF | Favorites | |
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