CNO at the surface of low and intermediate MS stars 1
نویسنده
چکیده
Recent studies of spectral lines of the CNO elements in the Sun and unevolved disk and halo stars show that most published abundance data may be affected by systematic errors due to inadequate 1D modelling of stellar atmospheres. This raises doubts about previously derived trends of CNO abundances as a function of [Fe/H]. In this review we concentrate on abundance ratios derived from weak spectral features with similar dependences on temperature and pressure, which ratios are then relatively insensitive to 3D model atmosphere effects and to Teff and surface gravity. The recent controversy about the trend of [O/Fe] vs. [Fe/H] is discussed, new results for C/O ratios as determined from forbidden lines and high excitation neutral lines are presented, and N/C ratios derived from NH and CH lines are commented on.
منابع مشابه
CNO elements
Using the standard infall model of Galactic chemical evolution, we explore the origin of carbon and calculate the abundance evolution of CNO elements for 8 different models of stellar nucleosynthesis yields. The results show that, in the early stage of the Galaxy, massive stars are the main producer of carbon, and that as our Galaxy evolves to the late stage, the longer lived intermediate-and l...
متن کاملYields from Low Metallicity, Intermediate Mass Agb Stars: Their Role for the Cno and Lithium Abundances in Globular Cluster Stars
We present the results of extensive computation of the Thermal Pulse phase AGB evolution of stars of metallicities in mass fraction 2 10 ?4 Z 0:01, for those masses in the range 2:5 M=M 6, which suuer the Hot Bottom Burning (HBB) phase. The evolution is fully computed, by assuming a mass loss rate consistent with the observations of the Magellanic Clouds lithium rich stars, and modelling convec...
متن کاملNova nucleosynthesis and Galactic evolution of the CNO isotopes
In this paper we study the role played both by novae and single stars in enriching the interstellar medium of the Galaxy with CNO group nuclei, in the framework of a detailed successful model for the chemical evolution of both the Galactic halo and disc. First, we consider only the nucleosynthesis from single low-mass, intermediate-mass and massive stars. In particular, the nucleosynthesis pres...
متن کاملCNO in Low- and Zero-Metallicity AGB Stars
The oldest stars hide information about the chemical evolution of the early universe. In this contect new models of the AGB stellar evolution phase at very low and zero metallicity are presented. Due to the deficiency or absence of CNO catalytic material hydrogen burning operates at significantly higher temperatures than in stars of higher metallicity. As a result convective mixing plays a very...
متن کاملEvolution of the First Stellar Generations
Although the theoretical study of very low metallicity (Z) and metal–free stars is not new, their importance has recently greatly increased since two related fields have been developing rapidly. The first is cosmological simulations of the formation of the first stars and of the reionisation period. The second is the observations of extremely metal poor stars. In this paper, we present pre–supe...
متن کامل