Very low-metallicity massive stars: - Pre-SN evolution models and primary nitrogen production

By R. Hirschi. 2006

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Context. Precise measurements of the surface abundances of extremely low-metallicity stars have recently been obtained, and they provide new constraints for the stellar evolution models. Aims. Stellar evolution models were computed in order to explain the surface abundances observed, in particular of nitrogen. Methods. Two series of models were computed. The first series consists of 20 $M_\odot$ models with varying initial metallicity ($Z=0.02$ down to $Z=10^{-8}$) and rotation ($\rm \upsilon_{ini}=0{-}600$ km s -1 ). The second one consists of models with an initial metallicity of $Z=10^{-8}$, masses between 9 and 85 $M_\odot$, and fast initial rotation velocities ($\rm \upsilon_{ini}=600{-}800$ km s -1 ). Results. The most interesting models are those with $Z=10^{-8}$ ([ Fe/H$]\sim-6.6$). In the course of helium burning, carbon and oxygen are mixed into the hydrogen-burning shell. This boosts the importance of the shell and causes a reduction of the CO core mass. Later in the evolution, the hydrogen shell deepens and produces a large amount of primary nitrogen. For the most massive models ($M\ga 60$ $M_\odot$), significant mass loss occurs during the red supergiant stage. This mass loss is due to the surface enrichment in CNO elements via rotational and convective mixing. The 85 $M_\odot$ model ends up as a WO-type Wolf-Rayet star. Therefore the models predict SNe of type Ic and possibly long and soft GRBs at very low metallicities. The rotating 20 $M_\odot$ models can best reproduce the observed CNO abundances at the surface of extremely metal-poor (EMP) stars and the metallicity trends when their angular momentum content is the same as at solar metallicity (and therefore have an increasing surface velocity with decreasing metallicity). The wind of the massive-star models can reproduce the CNO abundances of the most metal-poor carbon-rich star known to date, HE1327-2326.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ba5545a382352012f9a240b7d87828319665290a

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Citations in the corpus

The Origin of Elements from Carbon to Uranium (2020, background): “Stellar rotation induces mixing of C into the H-burning shell, producing a large amount of primary nitrogen, which is mixed back into the He-burning shell (Meynet & Maeder 2002; Hirschi 2007).”
Near-Field Cosmology with Extremely Metal-Poor Stars (2015, background): “5.3.6 Zero-metallicity, rotating, massive (∼ 60M⊙) and intermedi- ate mass (∼ 7M⊙) stars (Meynet, Ekström & Maeder 2006, Meynet et al. 2010 Hirschi 2007) Rotationally-driven meridional circulation leads to CNO enhancements and large excesses of 13C (and hence low 12C/13C values), Na, Mg, and Al,…”
s-process production in rotating massive stars at solar and low metallicities (2015, methodology): “In that study, the s-process production was investigated by assuming different concentrations of primary 22Ne in the convective He-burning core, guided by the early results of Hirschi (2007).”
THE MOST METAL-POOR STARS. IV. THE TWO POPULATIONS WITH [Fe/H] ≲ −3.0 (2012, background): “Zero-metallicity, rotating, massive (∼ 60 M⊙) and intermediate mass (∼ 7 M⊙) stars (Meynet et al. 2006, 2010; Hirschi 2007) Rotationally-driven meridional circulation leads to CNO enhancements and large excesses of13C (and hence low12C/13C values), Na, Mg, and Al, in material expelled in stellar…”
Chemical evolution with rotating massive star yields - I. The solar neighbourhood and the s-process elements (2018, background): “…that the aforementioned effects were not always studied with the same set of yields: effects (i) to (iii) were studied with yields mainly from Hirschi (2007), while effect (iv) with yields from Frischnecht (2011, PhD Thesis), Frischknecht et al. (2012) and Frischknecht et al. (2016), where…”
Europium production: neutron star mergers versus core-collapse supernovae (2013, methodology): “Here we adopt He, C, N and O yields from pre-supernova models of rotating massive stars from Meynet& Maeder (2002b), Hirschi et al. (2005), Hirschi (2007) and Ekström et al. (2008).”
Binarity in carbon-enhanced metal-poor stars (2014, background): “…and/or wind ejecta of Pop III stars where rotation of these stars plays a major role (e.g., Fryer, Woosley & Heger 2001; Meynet, Ekström & Maeder 2006; Chiappini et al. 2006; Karlsson 2006; Hirschi 2007; Chiappini et al. 2008; Meynet et al. 2010; Maeder & Meynet 2012; Cescutti et al. 2013).”