Core-Collapse Supernovae and Their Ejecta

Abstract

We present the detailed isotopic composition for 13, 15, 20, and 25 M_sun stars, based on induced super- nova calculations, which lead to explosive Si, 0, Ne, and C burning during the supernova outburst. The calculations made use of inferred mass cuts between the central neutron star and the ejected envelope by requiring ejected ⁵⁶Ni masses in agreement with supernova light curve observations. Specific emphasis is put on the treatment of the innermost layers, which experience complete Si burning with an alpha-rich freezeout and are the source of ⁵⁶Ni, the Fe group composition in general, and some intermediate-mass alpha elements like Ti. However, the uncertainty of the mass cut and the delay time between core collapse and the explosion via neutrino heating put limits on the possible accuracy. The predictions are compared with abundances from specific supernova observations (e.g., SN 1987A, 1993J) or supernova remnants (e.g., G292.O +1.8, N132D). The amount of detected ¹⁶O and ¹²C or products from carbon and explosive oxygen burning can constrain our knowledge of the effective ¹²C(α, γ)¹⁶O rate in He burning. The ⁵⁷Ni/⁵⁶Ni ratio (observed via y-rays from ^56,57Co decay or spectral features changing during the decay) can give constraints on Y_e in the innermost ejected zones. This helps to locate the position of the mass cut and to estimate the necessary delay time between collapse and explosion, in order to permit the required mass accretion ΔM_acc. Provided that the stellar precollapse models are reliable, this allows additional insight into the exact working of the supernova explosion mechanism. While this has been only possible for one supernova until present (SN 1987A, a 20 M_sun star), we can also compare the ejected composition from other progenitor masses to abundances in low-metallicity stars, which reflect the average Type II supernova composition, integrated over an initial mass function of progenitor stars.