Isotopes of C, N and O and chemical evolution of galaxies (II).
Abstract
Models of the chemical evolution of the Galaxy are examined which are not based on the instant recycling approximation. Recent observations of C, N, and O isotopic abundances are reported which confirm that C-12/C-13 ratios in the interstellar medium are about half the solar-system value, that N and O abundance gradients exist in spiral galaxies, and that more luminous stars have lower C-12/C-13 ratios. A formalism for analyzing the evolution of C, N, and O abundances without using the instant recycling approximation is outlined. This formalism is employed to investigate the evolution of the gas fraction, rates of nova and supernova explosions, and abundances as well as isotopic ratios of C, N, and O in two situations modeling the solar neighborhood and the galactic center. It is found that: (1) the evolution of C, N, and O abundances and isotopic ratios is well reproduced in the models considered; (2) stars of less than 5 solar masses have a greater influence on galactic chemical evolution than higher-mass stars after times of about 1 billion years; and (3) models with moderate infall of extragalactic matter give satisfactory results for the evolution of the C-12/C-13 ratio in both the solar neighborhood and the galactic center.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 1976
- Bibcode:
- 1976A&A....52....1V
- Keywords:
-
- Carbon Isotopes;
- Chemical Evolution;
- Galactic Evolution;
- Nitrogen Isotopes;
- Oxygen Isotopes;
- Abundance;
- Astronomical Models;
- Interstellar Matter;
- Solar System;
- Astrophysics