Coulomb corrections to the equation of state of nuclear statistical equilibrium matter: implications for SNIa nucleosynthesis and the accretion-induced collapse of white dwarfs

Coulomb corrections to the equation of state of degenerate matter are usual ly neglected in high-temperature regimes, owing to the inverse dependence o f the plasma coupling constant, Gamma, on temperature. However, nuclear sta tistical equilibrium matter is characterized by a large abundance by mass o f large-Z (iron group) nuclei. It is found that Coulomb corrections to the ion ideal gas equation of state of matter in nuclear statistical equilibriu m are important at temperatures T less than or similar to 5-10 x 10(9) K an d densities rho greater than or similar to 10(8) g cm(-3). At a temperature T = 8.5 x 10(9) K and a density rho = 8 x 10(9) g cm(-3), the neutronizati on rate is larger by greater than or similar to 28 per cent when Coulomb co rrections are included. However, the conductive velocity of a thermonuclear deflagration wave in C-O drops by similar to 16 per cent when Coulomb corr ections to the heat capacity are taken into account. The implications for S NIa models and nucleosynthesis, and also for the accretion-induced collapse of white dwarfs, are discussed. Particularly relevant is the result that t he minimum density for collapse of a white dwarf to a neutron star is shift ed down to 5.5-6 x 10(9) g cm(-3), a value substantially lower than previou sly thought.