On the oxygen isotopic composition of the Solar System

TL;DR

The paper investigates the origin of the Solar System's oxygen isotopic ratios, arguing that interstellar medium enrichment by AGB star winds and Galactic chemical evolution, rather than supernova pollution, explains observed differences.

Contribution

It proposes a new explanation for the Solar System's oxygen isotopic composition based on AGB star winds and Galactic chemical evolution, challenging previous supernova pollution models.

Findings

AGB star winds enrich the ISM with 17O-rich material.

Galactic chemical evolution follows a steeper trajectory than previously thought.

The model explains the difference in carbon isotope ratios between the Solar System and ISM.

Abstract

The 18O/17O ratio of the Solar System is 5.2 while that of the interstellar medium (ISM) and young stellar objects is ~4. This difference cannot be explained by pollution of the Sun's natal molecular cloud by 18O-rich supernova ejecta because (1) the necessary B-star progenitors live longer than the duration of star formation in molecular clouds; (2) the delivery of ejecta gas is too inefficient and the amount of dust in supernova ejecta is too small compared to the required pollution (2% of total mass or ~20% of oxygen); and (3) the predicted amounts of concomitant short-lived radionuclides (SLRs) conflicts with the abundances of 26Al and 41Ca in the early Solar System. Proposals for the introduction of 18O-rich material must also be consistent with any explanation for the origin of the observed slope-one relationship between 17O/16O and 18O/16O in the high-temperature components of primitive meteorites. The difference in 18O/17O ratios can be explained by enrichment of the ISM by the 17O-rich winds of asymptotic giant branch (AGB) stars, the sequestration of comparatively 18O-rich gas from star-forming regions into long-lived, low-mass stars, and a monotonic decrease in the 18O/17O ratio of interstellar gas. At plausible rates of star formation and gas infall, Galactic chemical evolution does not follow a slope-one line in an three-isotope plot, but instead moves along a steeper trajectory towards an 17O-rich state. Evolution of the ISM and star-forming gas by AGB winds also explains the difference in the carbon isotope ratios of the Solar System and ISM.