Insights Stellar Nucleosynthesis

This chapter briefly introduces the chemistry in circumstellar envelopes (CSE) around old, mass-losing stars. The focus is on stars with initial masses of one to eight solar masses that evolve into red giant stars with a few hundred times the solar radius, and which develop circumstellar shells several hundred times their stellar radii. The chemistry in the innermost circumstellar shell adjacent to the photosphere is dominated by thermochemistry, whereas photochemistry driven by interstellar UV radiation dominates in the outer shell. The conditions in the CSE allow mineral condensation within a few stellar radii, and these grains are important sources of interstellar dust. Micron-sized dust grains that formed in the CSE of red giant stars have been isolated from certain meteorites and their elemental and isotopic chemistry provides detailed insights into nucleosynthesis processes and dust formation conditions of their parent stars, which died before the solar system was bom 4.56 Ga ago. 

Evolved massive stars are associated with nebulae which result from the interaction of stellar winds and stellar ejecta with the ambient interstellar medium. By studying the chemical composition of these nebulae, together with their morphology, kinematics and total gas content, one can get insight into the previous evolutionary stages of the stars and unveil some of the nucleosynthesis and mixing processes occuring in their interiors. 

Fundamental to understanding the stars are measurements of distance and brightness, colour and constancy. Any theory of what stars are and how they behave must be able to explain these observations. Deeper insight is gained from measurements of chemical composition and the relationships between stars and the interstellar medium. The big story will show how elements are manufactured by nuclear reactions deep inside the stars - nucleosynthesis -and then transported to the stellar surface and into the interstellar medium. 

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