Nucleosynthesis - An Introduction. The Case of Classical Nova Explosions

The text presents a brief, historical introduction to the genesis of nuclear astrophysics, establishing links between the distribution of isotopic abundances in the Solar System and the nuclear processes that operate in stars. A number of suggestions and warnings to be taken into account for accurate numerical modeling in nuclear astrophysics are also outlined. The second part of the paper is devoted to classical nova outbursts, stellar explosions powered by thermonuclear runaways that take place in the H-rich accreted envelopes of white dwarfs in close binary systems. Extensive numerical simulations of nova outbursts have shown that the accreted envelopes attain peak temperatures ranging between 10(8) and 4x10(8) K, for about several hundred seconds, and therefore, their ejecta is expected to show signatures of a significant nuclear activity. Indeed, it has been claimed that novae can play a certain role in the enrichment of the interstellar medium through a number of intermediate-mass elements. This includes O-17, N-15, and C-13, systematically overproduced in huge amounts with respect to solar abundances, with a lower contribution in a number of other species with A < 40, such as Li-7, F-19, or Al-26.