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A two-parameter criterion for classifying the explodability of massive stars by the neutrino-driven mechanism
Thus far, judging the fate of a massive star (either a neutron star (NS) or a
black hole) solely by its structure prior to core collapse has been ambiguous.
Our work and previous attempts find a non-monotonic variation of successful and
failed supernovae with zero-age main-sequence mass, for which no single
structural parameter can serve as a good predictive measure. However, we
identify two parameters computed from the pre-collapse structure of the
progenitor, which in combination allow for a clear separation of exploding and
non-exploding cases with only few exceptions (~1-2.5%) in our set of 621
investigated stellar models. One parameter is M4, defining the normalized
enclosed mass for a dimensionless entropy per nucleon of s=4, and the other is
mu4 = d(m/M_sun)/d(r/1000 km) at s=4, being the normalized mass-derivative at
this location. The two parameters mu4 and M4*mu4 can be directly linked to the
mass-infall rate, Mdot, of the collapsing star and the electron-type neutrino
luminosity of the accreting proto-NS, L_nue ~ M_ns*Mdot, which play a crucial
role in the "critical luminosity" concept for the theoretical description of
neutrino-driven explosions as runaway phenomenon of the stalled accretion
shock. All models were evolved employing the approach of Ugliano et al. for
simulating neutrino-driven explosions in spherical symmetry. The neutrino
emission of the accretion layer is approximated by a gray transport solver,
while the uncertain neutrino emission of the 1.1 M_sun proto-NS core is
parametrized by an analytic model. The free parameters connected to the
core-boundary prescription are calibrated to reproduce the observables of
Supernova 1987A for five different progenitor models.Comment: 23 pages, 12 figures; accepted by ApJ; revised version considerably
enlarged (Fig. 7 and Sect.3.6 added
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