Grids of stellar models with rotation VII: Models from 0.8 to 300 M$_\odot$ at super-solar metallicity (Z = 0.020)

Abstract

We present a grid of stellar models at super-solar metallicity (Z = 0.020) extending the previous grids of Geneva models at solar and sub-solar metallicities. A metallicity of Z = 0.020 was chosen to match that of the inner Galactic disk. A modest increase of 43% (=0.02/0.014) in metallicity compared to solar models means that the models evolve similarly to solar models but with slightly larger mass loss. Mass loss limits the final total masses of the super-solar models to 35 M even for stars with initial masses much larger than 100 M . Mass loss is strong enough in stars above 20 M for rotating stars (25 M for non-rotating stars) to remove the entire hydrogen-rich envelope. Our models thus predict SNII below 20 M for rotating stars (25 M for non-rotating stars) and SNIb (possibly SNIc) above that. We computed both isochrones and synthetic clusters to compare our super-solar models to the Westerlund 1 (Wd1) massive young cluster. A synthetic cluster combining rotating and non-rotating models with an age spread between log 10 (age/yr) = 6.7 and 7.0 is able to reproduce qualitatively the observed populations of WR, RSG and YSG stars in Wd1, in particular their simultaneous presence at log 10 (L/L ) = 5-5.5. The quantitative agreement is imperfect and we discuss the likely causes: synthetic cluster parameters, binary interactions, mass loss and their related uncertainties. In particular, mass loss in the cool part of the HRD plays a key role.

The Formation of Globular Clusters as a Case of Overcooling

“…Suppressing supernova feedback for several million years has the effect of boosting the overall star formation efficiency (fraction of the gas turned into GC stars), allowing more 1G-processed material to become available for the formation of 2G stars. With only 3 Myr duration for the star formation phase, only binary components more massive than ∼ 100 M ⊙ would have had time to evolve off the main sequence (Yusof et al 2022), fill their Roche lobe, and deliver their processed envelopes. This would probably fall short of accounting for the required mass budget, whereas extending to a 10 Myr interval would allow stars down to ∼ 20 M ⊙ to contribute.…”