Revisiting Oxygen Production Pathways: 16O Abundances in 34 Metal-Poor Stars

We investigate how the oxygen isotope <sup>16</sup>O is produced in metal-poor stars and whether current nuclear reaction models can explain the oxygen abundances observed in such stars. Our study focuses on proton- and α-capture reactions operating within the Carbon–Oxygen–Fluorine (COF) nuclear reaction chain, using updated reaction rates from recent nuclear physics compilations. Oxygen abundances are calculated under representative stellar conditions and compared with observational measurements for a sample of 34 metal-poor halo and thick-disk stars taken from the literature. The results show that there exists a limited range of stellar temperatures for which the calculated oxygen abundances closely match the observed values. At relatively low temperatures, the oxygen abundance remains nearly constant, indicating that oxygen production and destruction are both inefficient. As the temperature increases beyond about 0.15 GK, oxygen production becomes more effective, leading to an increase in the predicted oxygen abundance. At still higher temperatures, competing nuclear reactions reduce the net amount of oxygen produced, causing the abundance to decline. A statistical comparison between the calculated and observed oxygen abundances shows a strong agreement, with a correlation coefficient of <i>r</i> = 0.89. For most stars, the differences between predicted and observed values are small and lie within the uncertainties expected from spectroscopic measurements. The few cases where larger differences are found can be explained by observational uncertainties and stellar mixing processes. Overall, our results indicate that the COF nuclear reaction chain provides a consistent explanation for oxygen production in low-mass, metal-poor stars and plays an important role in shaping the chemical evolution of the early Galaxy.