Filament Substructures and their Interrelation

The main structural components of solar filaments, their spines, barbs, and legs at the extreme ends of the spine, are illustrated from recent high-resolution observations. The thread-like structures appear to be present in filaments everywhere and at all times. They are the fundamental elements of solar filaments. The interrelation of the spines, barbs and legs are discussed. From observations, we present a conceptual model of the magnetic field of a filament. We suggest that only a single physical model is needed to explain filaments in a continuous spectrum represented by active region filaments at one end and quiescent filaments at the other end. 1. Filament Substructures A typical solar filament is composed of a spine, barbs, and two extreme ends. The spine defines the upper horizontal part of a filament. Barbs are lateral structures that extend from some of the spine to the chromosphere. The ends, also called “legs,” may be a collection of threads that appear to terminate at a single point or at multiple points. These components of filaments differ in appearance and relative importance in filaments in active regions, in quiescent filaments, and in “intermediate” filaments. “Intermediate” filaments are those between active region filaments and quiescent filaments, two categories at the extreme ends of the spectrum of filaments (Martin et al. 2007). Recent high-resolution observations obtained with the Swedish 1-m Solar Telescope (SST; Scharmer et al. 2003) show fine detail everywhere within filaments. Figure 1 illustrates the Southern end of a quiescent filament in the Southern hemisphere. In the upper panel, one can see many thin threads in both the spine and the barbs. Most of the threads are inclined with the main axis. The lower panel shows one end of the filament which looks like a “fish-tail”. Although, from the Catania Astrophysical Observatory (OACT) full-disk image (upper left corner of the image), the end structure seems to be more perpendicular to the filament main axis, the SST image shows that the fine threads that constitute the end are also aligned with the threads in the spine and the barbs. Such high-resolution Hα images demonstrate that filament spines, barbs and ends are all composed of thin threads. Seven pieces of observational evidence have been provided that filament threads are field aligned and their magnetic pointing can be deduced unambiguously in almost all cases with the supplementary use of magnetograms (Martin et al. 2007). The Hα movies made from Institute of Theoretical Astrophysics, University of Oslo, Norway Helio Research, 5212 Maryland Ave. La Crescenta, CA 91214, USA