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2.2 Formation rate

UpdateJump To The Next Update Information The AIC occurrence rate is difficult to determine for a number of reasons. These include incomplete understanding of binary star evolution and determining how much matter is truly accreted onto the white dwarf versus the amount that is ejected through novae  [48137234Jump To The Next Citation Point]. Another uncertainty is whether the collapse of an accreting Chandrasekhar mass white dwarf results in a supernovae explosion or a complete AIC (with accompanying neutron star formation). Figure 1View Image shows one estimate of the region in the space of initial white dwarf mass and accretion rate that produces AICs. New results continue to alter the dividing lines between these fates [234].
View Image

Figure 1: The final fate of accretion OMgNe white dwarfs as a function of the initial white dwarf mass and the accretion rate onto the white dwarf. (Figure 3 of [187]; used with permission.)
The AIC rate can be indirectly inferred from the observed amount of rare, neutron rich isotopes present in the Galaxy. These isotopes (formed via electron capture) are present in the portion (~ 0.1 Mo .) of the outer envelope ejected by the star during an AIC. The exact yield is sensitive to the neutron fraction in this ejecta, which depends both on the neutrino transport and the electron capture rates, but if all of these isotopes present in the Galaxy are assumed to have originated in AICs, an upper limit of -5 -1 ~ 10 yr can be set for the Galactic AIC rate [82Jump To The Next Citation Point].

Binary population synthesis analysis can be used to determine which accreting white dwarfs will undergo AIC. The results of Yungelson and Livio [268] predict that the galactic AIC rate is between 8 × 10- 7 and 8 × 10-5 yr-1. Thus, a reasonable occurrence rate can be found for an observation distance of 100 Mpc.


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