Grids of stellar models with rotation – V. Models from 1.7 to 120 M⊙ at zero metallicity

Abstract

Understanding the nature of the first stars is key to understanding the early Universe. With new facilities such as James Webb Space Telescope (JWST) we may soon have the first observations of the earliest stellar populations, but to understand these observations we require detailed theoretical models. Here we compute a grid of stellar evolution models using the Geneva code with the aim to improve our understanding of the evolution of zero-metallicity stars, with particular interest in how rotation affects surface properties, interior structure, and metal enrichment. We produce a range of models of initial masses (Mini) from $1.7$ to $120\, \mathrm{M}_{\odot }$, focusing on massive models of $9 \le M_{\rm ini}\le 120\, \mathrm{M}_{\odot }$. Our grid includes models with and without rotation, with rotating models having an initial velocity of 40 per cent of the critical velocity. We find that rotation strongly impacts the evolution of the first stars, mainly through increased core size and stronger H-burning shells during core He-burning. Without radiative mass loss, angular momentum builds at the surface in rotating models, thus models of initial masses $M_{\rm ini}\ge 60 \, \mathrm{M}_{\odot }$ reach critical rotation on the main sequence and experience mass loss. We find that rotational mixing strongly affects metal enrichment, but does not always increase metal production as we see at higher metallicities. This is because rotation leads to an earlier CNO boost to the H shell during He-burning, which may hinder metal enrichment depending on initial mass and rotational velocity. Electronic tables of this new grid of Population III models are publicly available.

The effects of surface fossil magnetic fields on massive star evolution: I. Magnetic field evolution, mass-loss quenching, and magnetic braking

“…This paper is part of a series in which we aim to explore the effects of surface fossil magnetic fields on massive star evolution. In the first paper of the series (Keszthelyi et al 2019, hereafter Paper I ), we used the Geneva stellar evolution code (Eggenberger et al 2008;Ekström et al 2012;Georgy et al 2013;Groh et al 2019;Murphy et al 2021) to explore the cumulative impact of magnetic mass-loss quenching, magnetic braking, and field evolution. In the second paper (Keszthelyi et al 2020, hereafter Paper II ), we implemented and studied massive star magnetic braking in the software instrument (Paxton et al 2011(Paxton et al , 2013(Paxton et al , 2015(Paxton et al , 2018(Paxton et al , 2019, detailing the magnetic and rotational evolution, and confronting the models with a sample of observed magnetic B-type stars from Shultz et al (2018).…”

Grids of stellar models with rotation VI: Models from 0.8 to 120 $M_\odot$ at a metallicity Z = 0.006

“…The present grid complements the grids already published for metallicities Z=0.014 (papers I and II, Ekström et al 2012;Georgy et al 2012), Z = 0.002 (paper III, Georgy et al 2013), Z = 0.0004 (paper IV, Groh et al 2019), and Z = 0 (paper V, Murphy et al 2021). The physical ingredients used are identical in all these grids, which only differ by the initial chemical composition adopted.…”

“…The present grid of stellar models complements the grids at Z = 0.014, 0.002, 0.0004 and Z = 0 (Ekström et al 2012;Georgy et al 2012Georgy et al , 2013Groh et al 2019;Murphy et al 2021). Together these models allow the exploration of the impact of changing the metallicity, the initial mass and the initial composition over large domains, keeping the other ingredients of the stellar models constant.…”

Massive Star Modeling and Nucleosynthesis

“…The time needed to produce enough carbon is longer for less massive stars, and gets ever shorter for more massive stars. Between 20 and 25 M ⊙ , the CNO cycle starts directly on the ZAMS (Siess et al, 2002;Ekström et al, 2008;Murphy et al, 2021) and no main sequence "knee" is visible FIGURE 4 | HR diagram for 9 M ⊙ models at different metallicities: Z = 0.014 (Ekström et al, 2012), Z = 0.002 (Georgy et al, 2013a), Z = 0.0004 (Groh et al, 2019), and Z = 0 (Murphy et al, 2021). The beginning and end of fusion phases are marked with a circle and a cross respectively (gray: H burning; black: He burning).…”