Jonathan Braithwaite, Matteo Cantiello
Weak magnetic fields have recently been detected in Vega and Sirius. Here, we
explore the possibility that these fields are the remnants of some field
inherited or created during or shortly after star formation and, unlike true
fossil fields, are still evolving as we observe them. The timescale of this
evolution is given in terms of the Alfven timescale and the rotation frequency
by tau_evol ~ tau_A^2 Omega, which would be comparable to the age of the star.
It is shown that it is likely that all intermediate- and high-mass stars
contain fields of at least the order of the strength found so far in Vega and
Sirius. Faster rotators are expected to have stronger magnetic fields. Stars
may experience an increase in field strength during their early main-sequence,
but for most of their lives field strength will decrease slowly. The length
scale of the magnetic structure on the surface may be small in very young stars
but should quickly increase to at least very approximately a fifth of the
stellar radius.
View original:
http://arxiv.org/abs/1201.5646
No comments:
Post a Comment