SIMBAD references

Primitive meteorites contain presolar grains that originated in stellar outflows and supernova ejecta. Low-density graphite grains from the Murchison carbonaceous meteorite were analyzed for the isotopic compositions of C, N, O, Mg, Si, K, Ca, and Ti by ion microprobe mass spectrometry. The grains are characterized by a large range of ¹²CM¹³C ratios (from 3.6 to 7200 compared to the solar ratio of 89), excesses in ¹⁵N (¹⁵NM¹⁴N up to 10 times solar) and ¹⁸O (¹⁸OM¹⁶O up to 185 times solar), large inferred ²⁶AlM²⁷Al ratios (from ²⁶Mg excesses) ranging up to 0.15, a large range in Si isotopic ratios (from 50% deficits in ²⁹Si and ³⁰Si relative to ²⁸Si up to more than 120% excesses), large excesses in ⁴¹K and ⁴⁴Ca from the prior presence of now-extinct ⁴¹Ca (T_1M2=10⁵ yr) and ⁴⁴Ti (T_1M2=59 yr), respectively, and excesses in ⁴²Ca, ⁴³Ca relative to ⁴⁰Ca, and ⁴⁹Ti, and ⁵⁰Ti relative to ⁴⁸Ti.

Several of these isotopic signatures indicate a supernova origin. In particular, the initial presence of ⁴⁴Ti and excesses of ²⁸Si as well as the size of the inferred ⁴¹CaM⁴⁰Ca ratios are proof that the carrier grains formed in supernova ejecta. We explored the possibility that the low-density graphite grains originated from C-rich ejecta of Type II supernovae. In such stars ⁴⁴Ti and ²⁸Si are produced in the inner layers and the presence of these two isotopes in carbonaceous grains is evidence for extensive mixing of different supernova layers in the explosion. We performed mixing calculations of different layers of the SN models by Woosley & Weaver under the imposed boundary condition that C≥O and compare the resulting isotopic ratios with the isotopic ratios measured in the meteoritic grains. The mixing model can explain the observed ¹²CM¹³C, ¹⁶OM¹⁸O, ³⁰SiM²⁸Si, and ⁴⁴Ti and ⁴¹Ca fairly well as long as jets of material from the Si-rich zone, carrying ⁴⁴Ti and pure ²⁸Si, are assumed to penetrate the O-rich zone and are ejected into and mixed with the C-rich layers, where carbonaceous grains can form, without overwhelming these layers with the massive amounts of oxygen. Problems with the model are that it produces not enough ¹⁵N and consistently yields lower ²⁹SiM³⁰Si ratios than those in the grains. Furthermore, large excesses in ⁴²Ca and ⁵⁰Ti found in several grains, which can be attributed to neutron capture, in the model are obtained only in layers with O>C. It remains to be seen whether adjustment of cross sections and/or multidimensional SN models can overcome some of these problems. It also remains to be seen whether Type Ia supernovae, which have been proposed as a source of SN grains in meteorites, can provide a better explanation. The fact that essentially all supernova grains identified so far are diamond, graphite, SiC of Type X and Si₃N₄, and only one oxide grain with a supernova signature has been found remains a puzzle.