Formation of a filament around a magnetic region

Abstract

The evolution of the active region AR4682 observed in 1985 during six rotations was dominated by three different phenomena:

• . the large scale pattern activity: relationship between two active regions, formation of a quiescent filament during the decay phase of the active region,

• . the presence of two pivot points along the filament surrounding the sunspot-with the long term one is associated the existence of the filament, with the short term one the activity with partial disappearance,

• . the magnetic shear during one rotation.

The magnetic field lines have been extrapolated from photospheric data using Alissandrakis code (1981). The magnetic configuration with the existence of a dip favors the formation of a filament. We note that the shearing of the sunspot region and of the filament are both well described by force-free magnetic fields with the same constant α. This suggests that they are both a consequent of the same shear process.