Triggering carbon burning in stars. Main reaction rates revised

Carbon burning determines the destiny of stars with masses higher than ≈ 8 M_⊙ and mass-accreting white dwarfs (WDs) in close binary systems. For this reason, in order to understand several astrophysical phenomena it is necessary to understand this key evolutionary phase; examples include determining the mass limits of CO and ONe WDs, the rates of e-capture, core-collapse, and Type Ia supernovae, and the contribution of massive stars to the chemical evolution. Despite its fundamental importance in astrophysics, the rate of the leading fusion process -- the ç reaction -- remains largely uncertain at relevant stellar temperatures. Revision of the ç reaction rate of both the α and the p channels and evaluation of the consequent impact on star models of mass ranging between 8 and 20 M_⊙. Based on the latest direct measurements of the ç cross section in the 2.8 to 4 MeV energy range, we calculated two new lower bounds for the rate of the ç process. These two estimates are obtained using different assumptions for the low-energy extrapolation of the modified astrophysical S^*(E) factor: one replacing the method adopted by , and another based on a hindrance model. CF88 caughlan_1988 The new rates are substantially lower than that commonly used in current stellar models of massive stars and accreting WDs. Specifically, the ratio between the new rate calculated in this work and the rate adopted in CF88 is, at T = 1 GK, 0.2 for the p channel and 0.085 for the α channel. Consequently, the characteristic carbon-burning temperatures and densities shift to higher values than those previously reported and the corresponding lifetime is significantly reduced. The maximum mass for progenitors' pure CO WDs is higher as well as the maximum CO WD mass. Moreover, in a 20 M_⊙ model close to central Si depletion, the physical structure of the core is less dense in the region between 2 and 4 M_⊙ from the center. This fact should have important consequences for the resulting explosive properties.