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Preprint typeset using L ATEX style emulateapj v. 04/03/99 HYPERCRITICAL ADVECTION DOMINATED ACCRETION FLOW

By H. A. Bethe, G. E. Brown and C. -h. Lee


In this note we study the accretion disc that arises in hypercritical accretion of ˙ M ∼ 10 8 MEdd onto a neutron star while it is in common envelope evolution with a massive companion. Such a study was carried out by Chevalier (1996), who had earlier suggested that the neutron star would go into a black hole in common envelope evolution. In his later study he found that the accretion could possibly be held up by angular momentum. In order to raise the temperature high enough that the disc might cool by neutrino emission, Chevalier used a small value of the α-parameter, where the kinematic coefficient of shear viscosity is ν = αcsH, with cs the velocity of sound and H the disc height; namely, α ∼ 10 −6. This resulted in gas pressure dominating. Using larger, more reasonable, α’s, α ∼ 0.1, although our results would not change for a wide range of α, we find the pressure to be radiation dominated with the result that temperatures of the accreting material are much lower, less than ∼ 0.5 MeV. The result is that neutrino cooling during the flow is negligible, satisfying very well the advection dominating conditions

Year: 2008
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