On the Dissociation Equilibrium of H2 in Very Cool, Helium-Rich White Dwarf Atmospheres

摘要

We investigate the dissociation equilibrium of $\rm H_2$ in very cool,helium-rich white dwarf atmospheres. We present the solution of the non-idealchemical equilibrium for the dissociation of molecular hydrogen in a medium ofdense helium. We find that at the photosphere of cool white dwarfs of $T_{\rmeff}\rm=4000 K$, the non-ideality results in an increase of the mole fractionof molecular hydrogen by up to a factor of $\sim 10$, compared to theequilibrium value for the ideal gas. This increases the $\rm H_{2}-He$ CIAopacity by an order of magnitude and will affect the determination of theabundance of hydrogen in very cool, helium-rich white dwarfs.