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2006MNRAS.370..629D - Mon. Not. R. Astron. Soc., 370, 629-644 (2006/August-1)
The surprising magnetic topology of τ Sco: fossil remnant or dynamo output?
DONATI J.-F., HOWARTH I.D., JARDINE M.M., PETIT P., CATALA C., LANDSTREET J.D., BOURET J.-C., ALECIAN E., BARNES J.R., FORVEILLE T., PALETOU F. and MANSET N.
Abstract (from CDS):
Despite the slow rotation rate of τ Sco, we none the less succeed in reconstructing the large-scale structure of its magnetic topology. We find that the magnetic structure is unusually complex for a hot star, with significant power in spherical-harmonic modes of degree up to 5. The surface topology is dominated by a potential field, although a moderate toroidal component is probably present. We fail to detect intrinsic temporal variability of the magnetic structure over the 1.5-yr period of our spectropolarimetric observations (in agreement with the stable temporal variations of the UV spectra), and infer that any differential surface rotation must be very small.
The topology of the extended magnetic field that we derive from the photospheric magnetic maps is also more complex than a global dipole, and features in particular a significantly warped torus of closed magnetic loops encircling the star (tilted at about 90° to the rotation axis), with additional, smaller, networks of closed-field lines. This topology appears to be consistent with the exceptional X-ray properties of τ Sco and also provides a natural explanation of the variability observed in wind-formed UV lines. Although we cannot completely rule out the possibility that the field is produced through dynamo processes of an exotic kind, we conclude that its magnetic field is most probably a fossil remnant from the star formation stage.
Abstract Copyright: 2006 The Authors. Journal compilation © 2006 RAS
Journal keyword(s): techniques: polarimetric - stars: early-type - stars: individual: τ Sco - stars: magnetic fields - stars: rotation - stars: winds, outflows
Simbad objects: 9
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