Nucleosynthesis helium burning

Hoyle successfully predicts existence of a 7.6 MeV resonance state of the carbon-12 nucleus on grounds that otherwise little carbon would survive further processing into oxygen during stellar nucleosynthesis by helium burning, whereas in fact the C/O ratio is about 0.5. Discovery of strange particles. 

There are several lines of evidence that nucleosynthesis takes place in stars. The compositions of the outer envelopes of evolved low- and intermediate-mass stars show enhancements of the products of nuclear reactions (hydrogen and helium burning and s-process nucleosynthesis, as defined below). The ejecta of supemovae (stellar explosions) are highly enriched in short-lived radioactive nuclides that can only have been produced either just before or during the explosion. At the other extreme, low-mass stars in globular clusters, which apparently formed shortly after the universe formed, are deficient in metals (elements heavier than hydrogen and helium) because they formed before heavy elements were synthesized. 

Primary nucleosynthesis Some astronomical evidence suggests that 13C nucleosynthesis has a primary component that is, a production rate in stars that does not rely on the prior presence of carbon in the interstellar gas from which the stars formed (see below). This is attested to by nitrogen also having a primary component (see 14N). This can occur in a red AGB star, which is creating new 12C by the triple-alpha process in a helium-burning shell beneath its H-containing envelope. Such stars undergo... 

Type la supernovae offer an alternative explanation for the isotopic signature of X grains. In the model by Clayton et al. (1997) nucleosynthesis takes place by explosive helium burning of a helium cap on top of a white dwarf. This process produces most of the isotopic signatures of the SN grains. The isotopes Al, Si, and " " Ti... 

It is on the TP-AGB that the richest nucleosynthesis occurs for low and intermediate-mass stars, even though stars spend such a short amount of time there compared to previous evolutionary phases. The nucleosynthesis is driven by thermal instabilities of the helium-burning shell, reviewed in Sect. 4. Of particular importance is the action of repeated third dredge-up events that mix the products of He-burning to the stellar surface. Material from the He-shell will become part of the next hydrogen shell, where they will experience proton captures during the next interpulse period. For this reason, not only do we need to consider nucleosynthesis in the thermal pulse itself but also... 

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