Nucleosynthesis in stars

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. 

The energy released by nuclear reactions provides the power that causes stars, including our Sun, to shine. The realization that stars are fueled by nuclear reactions was key to understanding the long lifetimes of stars and to reconciling the age of the Sun with the age of the Earth (see Box 3.1). The energy budget of a star represents a balance between 

Essentially all theories of the formation of the solar system since those of Immanuel Kant (1755, Allgemeine Naturgeschichte un Theorie des Himmels) and Pierre LaPlace (1796, Exposition du system du monde) have assumed that the Earth and Sun formed at approximately the same time. Our modern view holds that the solar system formed 4.568 billion years ago in a single event and that the Sun is about half way through its life. 

There are several bodies of information that feed into our understanding of stellar nucleosynthesis. We will start with a discussion of the classification of stars, their masses and mass distributions, and their lifetimes. From this information we can assess the relative importance of different types of stars to the nucleosynthesis of the elements in our solar system and in the galaxy. We will then discuss the life cycles of stars to give a framework for the discussion of nucleosynthesis processes. Next, we will review the nuclear pathways 

The details of stellar nucleosynthesis are a strong function of stellar mass (see below). Stars range in mass from -0.08 to -120 solar masses (abbreviated M ). The low-mass 

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This chapter presents an updated report of the data with necessarily some limitations, but I will try to keep the most striking features and highlight the clearest relation with nucleosynthesis in stars. 

An extensive elaboration of HFB was published in the October issue of Reviews of Modern Physics. This was the now famous B FH. A1 Cameron had already published his article in the June issue of the Publication of the Astronomical Society of the Pacific, but they were unaware of his work when they had submitted their manuscript to Reviews of Modern Physics at about that date. Cameron s article referred to HFB but Fowler points out that it was nevertheless a remarkable feat for one person to arrive at the same conclusions as four who had worked very hard and in concert. B FH attracted much attention and convinced people that nucleosynthesis in stars had been understood quantitatively. 

Well, not quite everything. The hght elements lithium, beryllium, and boron are formed mostly by the break-up of heavier nuclei when hit by cosmic rays and other high-energy particles in interstellar space. This process, which whittles the nuclei down to hghter elements, is called spallation. Nucleosynthesis in stars produces very httle of these three elements. 

The contents of this chapter will be the foundation of all subsequent discussions. Your depth of understanding of each of these subjects will grow as you continue through the book, but it is critical to have a grasp of these basic ideas before moving ahead. In the next chapter we will discuss the origin of the elements via nucleosynthesis in stars. 

Woodstock is also sung by Crosby, Stills, Nash, and Young on their album Deja Vu. For a wonderful overview of nucleosynthesis in stars, see Marcus Chown, The Magic Furnace The Search for the Origins of Atoms (New York Oxford University Press, 2001). 

The approximation of thermal equilibrium played an important role in the initial formulation of the theory of nucleosynthesis in stars. Fred Hoyle showed in 1946 that stellar centers may achieve temperatures in which thermal equilibrium can be... 

The three isotopes of oxygen are produced by nucleosynthesis in stars, but by different nuclear processes in different stellar environments. The principal isotope, is a primary isotope... 

Production of radioactive beams for the synthesis of heavy nuclei and for the questions of the nucleosynthesis in stars... 

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