Zero and Extremely Low-metallicity Rotating Massive Stars: Evolution, Explosion, and Nucleosynthesis Up to the Heaviest Nuclei

Abstract

We present the evolution and the explosion of two massive stars, 15 and 25 M ⊙, spanning a wide range of initial rotation velocities (from 0 to 800 km s−1) and three initial metallicities: Z = 0 ([Fe/H] = −∞), 3.236 × 10−7 ([Fe/H] = −5), and 3.236 × 10−6 ([Fe/H] = −4). A very large nuclear network of 524 nuclear species extending up to Bi has been adopted. Our main findings may be summarized as follows: (a) rotating models above Z = 0 are able to produce nuclei up to the neutron closure shell N = 50, and in a few cases up to N = 82; (b) rotation drastically inhibits the penetration of the He convective shell in the H-rich mantle, a phenomenon often found in zero metallicity nonrotating massive stars; (c) vice versa, rotation favors the penetration of the O convective shell in the C-rich layers with the consequence of significantly altering the yields of the products of the C, Ne, and O burning; (d) none of the models that reach the critical velocity while in H burning lose more the 1 M ⊙ in this phase; (e) conversely, almost all models able to reach their Hayashi track exceed the Eddington luminosity and dynamically lose almost all their H-rich mantle. These models suggest that rotating massive stars may have contributed significantly to the synthesis of the heavy nuclei in the first phase of enrichment of the interstellar medium, i.e., at early times.

Presupernova Evolution and Explosive Nucleosynthesis of Rotating Massive Stars. II. The Supersolar Models at [Fe/H] = 0.3

“…As already mentioned in Section 1, the stirring of matter between the core-He burning and the H-shell burning (a phenomenon that we call entanglement; Roberti et al 2024), is responsible for the substantial production of primary N, F, and neutron-capture nuclei. Since the entanglement may operate only if an active H-burning shell is present and since all rotating models lose their H-rich mantle during their central He-burning phase, the efficiency of the synthesis of all these nuclei depends on the lifetime of the H-burning shell in He burning: the stronger the mass loss, the faster the evaporation of the mantle, the smaller the synthesis of N, F, and neutronrich nuclei.…”

“…Those results were mainly intended as a database to be used in galactic chemical evolution (GCE) models (e.g., Prantzos et al 2018;Palla et al 2022;Vasini et al 2022;Pignatari et al 2023;Prantzos et al 2023;Womack et al 2023). In an additional paper (Roberti et al 2024) we explored the influence of rotation on the evolution and nucleosynthesis of massive stars also at metallicities between primordial (Z = 0) and [Fe/H] = −4. An obvious extension of these surveys is the study of supersolar metallicity (SSM) models and therefore we present models here with an initial metallicity [Fe/H] = 0.3 and with the same grid of initial masses and rotation velocities as the LC18 database.…”

“…Meynet & Maeder (2002) were the first to discuss the nitrogen enhancement in rotating massive stars. Later on, following the exploratory work by Pignatari et al (2008), many groups studied how the primary synthesis of 14 N in rotating massive stars leads to 22 Ne and therefore to the production of neutron-capture elements, for a broad range of initial masses, initial rotation velocities, and initial metallicity (see, e.g., Frischknecht et al 2012Frischknecht et al , 2016Choplin et al 2018;Banerjee et al 2019;Roberti et al 2024). LC18 were the first to provide an extended set of homogeneous yields coming from the evolution and explosion of massive stars in the range 13-120 M e .…”

Impact of Newly Measured Nuclear Reaction Rates on 26Al Ejected Yields from Massive Stars

“…The adopted initial composition for the solar metallicity is the one provided by Asplund, 2009 [28] and corresponds to Z = 0.01345. For the simulations, we used an extended nuclear network, already adopted in Roberti et al [29], including 525 nuclear species extending up to Bi and more than 3000 reactions, fully coupled to the solution of the equations that describe the evolution of the star. The explosion and the associated explosive nucleosyntheses have been computed by means of the HYPERION Lagrangian hydrodynamic flux limited diffusion radiation 1D code (extensively described in [30]).…”

“…To evaluate the impact of the newly measured reaction rates on 26 Al, we calculated the evolution of a 20 M ⊙ star at solar metallicity adopting three different reaction rate selections for the 25 Mg(p, γ) 26 Al, 26 Al(p, γ) 27 Si, 26 Al(n, p) 26 Mg and 26 Al(n, α) 23 Na nuclear reaction, as summarised in Table 1. The nuclear reaction rates adopted in the STANDARD case are the same as in [29]; in particular, the 25 Mg(p, γ) 26 Al and 26 Al(p, γ) 27 Si reaction rates are both from [32], while the 26 Al(n, p) 26 Mg and 26 Al(n, α) 23 Na reaction rates are from [33,34], respectively. In the LA-BA case abbreviation for "LAIRD-BATTINO"), the 26 Al(n, p) 26 Mg and 26 Al(n, α) 23 Na reaction rates are both from [21], while the 25 Mg(p, γ) 26 Al and 26 Al(p, γ) 27 Si reaction rates are both from [2].…”