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Like ancient Gaul, abundance data relevant to the study of nucleosynthesis in the course of stellar and galactic evolution can be broadly divided into three parts: abundances of the various elements and their isotopes in the Solar System; composition peculiarities in the visible layers of individual stars, planetary nebulae, young supernova remnants, cosmic ray sources, etc. due to thermonuclear (or other) processes that have taken place in the course of the internal evolution of the stars themselves ; and the com position of the interstellar medium (ISM) at different places and times as judged either from direct observations of the ISM at the present time or from characteristics of the various stellar populations that are taken as being identical to those of the ISM at the time and place where the respective stars were born. The Solar System provides the richest source of data that we have, thereby giving us both a cross section through the effects of past nucleo synthesis in the neighborhood of the Sun and a standard to which the more limited data for other objects can be compared; while abundances in evolved stars, planetary nebulae, and young supernova remnants (SNR) provide direct information on nuclear and mixing processes in stellar evolution that are believed to be responsible for continuing enrichment of
Pagel et al. (Tue,) studied this question.