Some Recent Results from Galactic and Stellar Evolution Theory

Abstract

Recent progress in stellar and galactic evolution theory give excellent agreement between observational abundances and the theoretical yields for elements heavier than helium. This includes the secondary production of 14 N and the variation of N/O over the face of M101 which was observed by Searle. Subject headings: abundances-galactic structure-nucleosynthesis-stellar evolution I. INTRODUCTION In two recent papers (Talbot and Arnett 1973a, b; hereafter called TA73a and TA736, respectively) we have discussed models of the chemical evolution of galaxies. The theory of stellar evolution and explosive nucleosynthesis is progressing at a rapid pace, and we wish to present here some results for chemical evolution which are more detailed than those in the two papers referred to above. We find that, under the same assumptions used by Arnett and Schramm (1973) to obtain agreement between the theoretical and observed cosmic-ray abundances , we obtain an excellent agreement between the theoretical heavy-element yield and that required by observational results. For more detail the references above should be examined; however, the most important assumptions are: (1) the weak interaction can be described (at least approximately) by a universal Fermi interaction, (2) the bulk of primary nucleosynthesis involves explosive ejection of matter from massive stars {M ^ 7 and (3) the abundances of «-particle nuclei (12 C, 16 0, etc.) in the mantle [M(r) > 1.4 M©] of the presupernova star are a reasonable approximation to those in the ejected debris. This last assumption is suggested by the structure of the evolutionary models of massive stars (7 ^ M/M© ^ 80) at the onset of core collapse, and will be discussed in more detail in a separate publication. Further, upon examining the production of 14 N we find that by using (1) galactic evolutionary models constrained only by properties of the solar neighborhood and (2) only secondary synthesis of 14 N from C and O, we obtain excellent quantitative agreement with observations of N/O across the disks of nearby galaxies. This result arises from the direct application of the stellar evolutionary calculations of Iben and Paczyñski (see TA73a, b for detailed references).