Filamentary Structure in Solar Prominences.

We have computed isobaric steady-state models of prominence filamentary structure similar to the models of Orral and Zirker. The models have cylindrical symmetry and contain uniform longitudinal magnetic fields. Thermal conduction transverse to the field balances the net gain or loss of radiative energy at each point of the filament. To obtain models with central temperatures lower than Orral and Zirker's 30000 K we have included an approximate treatment of radiative transfer in the resonance lines of H I, He I, and He ii. We have also included radiative losses from heavy ions and the effects of absorption of chromospheric and coronal radiation. We find that filaments of observable width are possible for certain values of the axial temperature. At densities corresponding to NrT = 2 X 1013, 2 >c 10' , 2 X 1015, respectively, the axial temperature must lie near 15600 , t2100 , and 9600 K. Our models of wide filaments have broad, almost-isothermal, central regions. The temperature rise to the corona occurs in a thin shell. That part of the filament below 30000 K is stable against temperature perturbations if the magnetic field has a strength of at least 1 gauss. Above 30000 K in the shell, the conditions for stability continue to hold if the mean free path of the neutral particles remains small compared with the shell thickness. The shells of our models become very thin for magnetic fields H > 1 gauss. We cannot say, without further investigation of the heat transport and the mechanism that heats the normal corona, whether real filaments are entirely stable. Stability considerations alone do not set a satisfactory upper limit on the width of filaments. We discuss the possibility that filament size depends on a balance of the radiative losses in the shell with the energy available to heat the corona.