Fig. 2.
Equilibrium electric potential as a function of grain size: (a) graphite and (b) silicate. The solid lines are the W+06 model and the dashed lines are the WD01 model. The thick lines are the case with the spectral index of the radiation field p = 1 and the thin lines are the case with p = 5. Other assumed quantities are noted in the panels as the hydrogen density nH,-5 = nH/10-5 cm-3, the gas temperature T,4 = T/104 K, and the radiation intensity JL,-21 = JL/10-21 erg s-1 cm-2 Hz-1 sr-1. The dotted lines show the critical electric potential where the grain destruction occurs by the Coulomb explosion; the upper lines are the case with the tensile strength of 1011 dyn cm-2, and the lower lines are the case with 1010 dyn cm-2.