Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007apj...671l.189a&link_type=abstract
The Astrophysical Journal, Volume 671, Issue 2, pp. L189-L192.
Astronomy and Astrophysics
Astronomy
23
Magnetohydrodynamics: Mhd, Stars: Coronae, Stars: Flare, Stars: Magnetic Fields
Scientific paper
We present some new results showing that the flux cancellation model for coronal mass ejections (CMEs) works well also in a complex-topology magnetic field. We consider as a model problem the case of the flux-cancellation-driven evolution of a quadrupolar configuration. We find that (1) during the first phase, the field evolves slowly, with a twisted flux rope in equilibrium being created at some time; (2) nonequilibrium sets in at a critical time and the configuration experiences a major global disruption. These features are similar to those previously obtained for a bipolar configuration. Some differences between the two cases are however observed: (1) the presence of an X-point above the twisted flux rope makes the expulsion of the latter much easier due to the weaker confinement near this point; this difference may be at the origin of the existence of two classes of CMEs-fast and slow; (2) the energy W(t) of the configuration remains smaller than the energy Wσ(t) of the associated totally open field, and then the disruption does not occur when W(t)~Wσ(t), as in the bipolar case. Rather we get nonequilibrium when W(t)~WSO(t), where WSO(t) is the energy of a semiopen field which has its open lines connected to the two central spots on which flux cancellation is imposed. A consequence of our results is that the topological complexity of a preerupting configuration cannot be taken as a criterion for eliminating the flux cancellation model in favor of the well-known breakout model.
Aly Jean-Jacques
Amari Tahar
Linker Jon
Mikic Zoran
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