Is the magnetic field in quiescent prominences force-free?

Abstract

Aims. We describe under which conditions the magnetic fields of quiescent prominences are force-free and under which gravity plays the dominant role. Methods. The existing observational determinations of the magnetic field are summarised and the calculation of the plasma β is outlined. We derive the dependence of β on the prominence weight and the field strength. Results. We show that in many cases of well-developed quiescent prominences the field can deviate substantially from the force-free situation and gravity fully determines the structure of the magnetic dips.