The magnetic field in a protostellar cloud

Abstract

General forms of theB-p relation are investigated in both the isothermal and the non-isothermal regions. The magnetic flux dissipation either by ambipolar diffusion or by Ohmic dissipation has been studied. The rates of heating due to the magnetic dissipation processes have been calculated in comparison with the rate of compressional heating. The magnetic field strength is derived as a function of flux/mass ratio, mass, density, and geometry of the isothermal cloud. In the non-isothermal region, the temperature is added to the above-mentioned variables. It has been found that the magnetic flux starts to dissipate via ambipolar diffusion at neutral density ofn>3×109 cm−3. Ambipolar diffusion continues effective until reaching densities ofn>1011 cm−3, where Ohmic dissipation dominates. Under some conditions, the electrons evaporate from the grain surface atn>1013 cm−3, while the ions are still adsorbed on the grain surfce. In this case, the magnetic flux loss returns to be influenced by ambipolar diffusion. The rates of heating by both Ohmic dissipation Γ OD and ambipolar diffusion Γ AD are found to be smaller than the rate of compressional heating Γ C in case of magnetic dissipation. Assuming that the magnetic field is frozen in the medium, then Γ C is smaller than both Γ OD and Γ AD . The above results of heating were found in the non-isothermal region.