1999/06/16 by Luciano Piersanti, L. Piersanti, S. Cassisi +5 · 2 citations
Physics and Astronomy · #Accretion (finance) #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Diffusion #Flash (photography) #Flashing #Gamma-ray bursts and supernovae #Helium #Hydrogen #Supernova #White dwarf #astro-ph
paper · pdf · doi:10.1086/312166
14 pages and 3 Postscript figures, Accepted for publication on ApJ Letters
arxiv created 1999/06/16 · openalex publication_date 1999/08/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Hydrogen-rich matter has been added to a carbon-oxygen white dwarf of initial mass 0.516 M ☉ at the rates 10 -8 and 2 × 10 -8 M ☉ yr -1 , and results are compared with those for a white dwarf of the same initial mass that accretes pure helium at the same rates. For the chosen accretion rates, hydrogen burns in a series of recurrent mild flashes and the ashes of hydrogen burning build up a helium layer at the base of which a helium flash eventually occurs. In previous studies involving accretion at higher rates and including initially more massive white dwarfs, the diffusion of energy inward from the hydrogen shell-flashing region contributes to the increase in the temperature at the base of the helium layer, and the mass of the helium layer when the helium flash begins is significantly smaller than in a comparison model accreting pure helium; the helium shell flash is strong enough to cause the model to expand beyond its Roche lobe, but not strong enough to develop into a supernova explosion. In contrast, for the conditions adopted here, the temperature at the base of the helium layer becomes gradually independent of the deposition of energy by hydrogen shell flashes, and the mass of the helium layer when the helium flash occurs is a function only of the accretion rate, independent of the hydrogen content of the accreted matter. Several thousand hydrogen shell flashes must be followed before the helium flash takes place. Because of the high degeneracy at the base of the helium layer, temperatures in the flashing zone will rise without a corresponding increase in pressure, nuclear burning will continue until nuclear statistical equilibrium is achieved, and structural evolution will proceed hydrodynamically; the model will become a supernova, but not of the classical Type Ia variety.