Massive Stars as Cosmic Engines through the Ages

TL;DR

This paper reviews the physics and models of massive stars, focusing on chemical enrichments, Wolf-Rayet star properties, and their evolution across different metallicities, highlighting implications for supernovae and gamma-ray bursts.

Contribution

It introduces updated model physics and discusses new insights into the chemical and evolutionary properties of massive stars, especially WR and WO stars, across varying metallicities.

Findings

(C+O)/He ratio is a better indicator of evolution for WC stars.

Lower metallicity regions have higher (C+O)/He ratios at the same luminosity.

WO stars likely originate from very high initial masses in low Z environments.

Abstract

Some useful developments in the model physics are briefly presented, followed by model results on chemical enrichments and WR stars. We discuss the expected rotation velocities of WR stars. We emphasize that the (C+O)/He ratio is a better chemical indicator of evolution for WC stars than the C/He ratios. With or without rotation, at a given luminosity the (C+O)/He ratios should be higher in regions of lower metallicity Z. Also, for a given (C+O)/He ratio the WC stars in lower Z regions have higher luminosities. The WO stars, which are likely the progenitors of supernovae SNIc and of some GRBs, should preferentially be found in regions of low Z and be the descendants of very high initial masses. Finally, we emphasize the physical reasons why massive rotating low Z stars may also experience heavy mass loss