Abstract

Poster - Splinter StellarEndpoints   (MW-2235)

The Critical Metallicity of Red Supergiant Formation

Po-Sheng Ou, Ke-Jung Chen
Academia Sinica Institute of Astronomy and Astrophysics (ASIAA)

Using extensive grids of stellar evolution models, we identify a critical metallicity of Z~0.001 for red supergiant (RSG) formation. Above this threshold, massive stars generally expand into RSGs during core-helium burning, whereas lower-metallicity stars tend to remain blue and compact. To investigate the physical origin of this transition, we perform controlled experiments by independently varying opacity and nuclear reaction rates. We find that metallicity strongly affects the stellar radius at the terminal-age main sequence (TAMS), which in turn determines the subsequent post-main-sequence evolutionary pathway. Models with sufficiently large TAMS radii are more likely to develop extended envelopes and evolve into RSGs. Our results provide a physical explanation for the metallicity dependence of RSG formation and its consequences for stellar mass loss.