The 14N(e -, nu ) 14C( alpha , gamma ) 18O Reaction and Helium Flashes in Accreting Helium White Dwarfs

The role of the NCO reaction in the He-flash evolution of He white dwarfs undergoing mass accretion is investigated by means of numerical simulations, considering accretion of (3-100) x 10 to the -10th solar mass/yr onto a 0.3-solar-mass star. At lower accretion rates, N-14 is completely converted to C-14, and the He-flash is triggered by the CO reaction once the central density has increased sufficiently; at 10 to the -8th solar mass/yr, however, the CO reaction immediately follows the NC reaction and is responsible for rapid heating, triggering the 3-alpha reaction and He flash at density as low as 1 Mg/cu cm. The He-flash density in both cases is significantly lower than in corresponding scenarios without the NCO reaction.