2006/09/07 by Rebecca G. Martin, R. G. Martin, Christopher A. Tout +3 · 2 citations
Physics and Astronomy · #Accretion (finance) #Astronomy and Astrophysical Research #Carbon fibers #Critical mass (sociodynamics) #Gamma-ray bursts and supernovae #Light curve #Mass transfer #Scientific Research and Discoveries #Stellar evolution #Supernova #Thermonuclear fusion #White dwarf #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2006.11019.x
published as Mon.Not.Roy.Astron.Soc.373:263-270,2006 · Accepted for publication in MNRAS
arxiv created 2006/09/07 · openalex publication_date 2006/10/20 · arxiv updated 2016/04/26 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Doubly-degenerate binary systems consisting of two white dwarfs (WDs) both composed of carbon and oxygen and close enough that mass is transferred from the less massive to the more massive are possible progenitors of Type Ia supernovae. If the mass-transfer rate is slow enough that the accreting WD can reach a mass of 1.38 M⊙, then it can ignite carbon degenerately at its centre. This can lead to a thermonuclear runaway and hence a supernova explosion. However, if the accretion rate is too high the outer layers of the WD heat up too much and carbon ignites there non-degenerately. A series of mild carbon flashes can then propagate inwards and convert the carbon to neon relatively gently. There is no thermonuclear runaway and no supernova. We examine the critical accretion rate at which ignition switches from the centre to the surface for a variety of WDs and find it to be about two-fifths of the Eddington rate. In a real binary star, the mass-transfer rate falls off as mass transfer proceeds and the system widens. Even if the initial transfer rate is high enough for carbon to ignite at the outer edge, if such rapid accretion were to persist, we find that it can extinguish if the rate drops sufficiently quickly. The interior of the WD remains carbon rich and, if sufficient mass can still be transferred from the companion, it can eventually ignite degenerately at the centre. The primary WD must be about 1.1 M⊙ or above and the companion about 0.3 M⊙. Though WDs of such low mass are expected to be pure helium, we note that a star of initial mass 2.5 M⊙ has a CO core of about 0.3 M⊙ when it begins to ascend the asymptotic giant branch. Alternatively, if the accretion rate can be limited to a maximum of 0.46 of the Eddington rate, then a 1.1-M⊙ WD accretes sufficiently slowly to explode from a companion WD of any large enough mass.