Progenitors of electron-capture supernovae

Abstract

Abstract. We investigate the lowest mass stars that produce Type-II supernovae, motivated by recent results showing that a large fraction of type-II supernova progenitors for which there are direct detections display unexpectedly low luminosity (for a review see e.g. Smartt 2009). There are three potential evolutionary channels leading to this fate. Alongside the standard 'massive star' Fe-core collapse scenario we investigate the likelihood of electron capture supernovae (ECSNe) from super-AGB (S-AGB) stars in their thermal pulse phase, from failed massive stars for which neon burning and other advanced burning stages fail to prevent the star from contracting to the critical densities required to initiate rapid electron-capture reactions and thus the star's collapse. We find it indeed possible that both of these relatively exotic evolutionary channels may be realised but it is currently unclear for what proportion of stars. Ultimately, the supernova light curves, explosion energies, remnant properties (see e.g. Knigge et al. 2011) and ejecta composition are the quantities desired to establish the role that these stars at the lower edge of the massive star mass range play.Keywords. stars: evolution, supernovae: general Preliminary modelsFor stars that develop degenerate ONe cores with M ONe 1.37M , neon is ignited off-centre. Such an ignition was also found in the models of Nomoto (1984), but the subsequent evolution was not followed to a conclusion. As we discuss below, the nucleosynthesis in these neon-burning shells becomes rather complex and the speed and nature of their inward propagation determine the evolutionary outcome.We computed a 9M model from pre-main sequence using the MESA code (Paxton et al. 2011). Following the main sequence and core He-burning, our model ignites carbon non-degenerately at its centre where the stellar material becomes convectively unstable, which is typical of a massive star with M ini /M 20. Following the ignition of convective secondary carbon burning shells, neon is ignited at the co-ordinate ∼ 0.75M away from the centre. Ignition takes place where the maximum temperature now resides due to a temperature inversion in the core caused by the onset of degeneracy following the central extinction of carbon.The centre contracts since there is no constant source of energy production there, only neutrino losses and URCA cooling. Meanwhile, energy production in the shell pushes the temperature there high enough to ignite oxygen, leaving behind mostly isotopes of Si and S. We find that the shell propagates by means of compressional heating, when 341 at https://www.cambridge.org/core/terms. https://doi

The Evolution of Compact Binary Star Systems

“…Figure 1 shows, as an example, the endpoints of stellar evolution for intermediate mass stars, computed by Siess [707, 708]. 7 Note, results of computations very strongly depend on still uncertain rates of nuclear burning, the treatment of convection, the rate of assumed stellar-wind mass loss, which is poorly known from observations for the stars in this transition mass range, as well as on other subtle details of the stellar models (see discussion in [599, 325, 98, 749]). For instance, zero-age main sequence (ZAMS) masses of solar-composition progenitors of ECSN found by Poelarends et al [599] are M 0 ≈ (9.0–9.25) M ⊙ 8.…”

The Evolution of Compact Binary Star Systems

“…3 Figure 1 shows, as an example, the endpoints of stellar evolution for intermediate mass stars, computed by Siess [700,701]. 4 Note, results of computations very strongly depend on still uncertain rates of nuclear burning, treatment of convection, the rate of assumed stellar wind mass loss, poorly known from observations for the stars in this transition mass range, as well as on other subtle details of stellar models (see discussion in [593,321,96,742]). For instance, ZAMS masses of solar composition progenitors of ECSN found by Poelarends et al [593] are M 0 ≈ (9.0 -9.25) M .…”