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Register a new userAluminium-26 from massive binary stars II. Rotating single stars up to core-collapse and their impact on the early Solar System
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Hannah E. Brinkman
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Radioactive nuclei were present in the early Solar System, as inferred from analysis of meteorites. Many are produced in massive stars, either during their lives or their final explosions. In the first paper in this series (Brinkman et al. 2019), we focused on the production of $^{26}$Al in massive binaries. Here, we focus on the production of another two short-lived radioactive nuclei, $^{36}$Cl and $^{41}$Ca, and the comparison to the early Solar System data. We used the MESA stellar evolution code with an extended nuclear network and computed massive (10-80 M$ _{odot} $), rotating (with initial velocities of 150 and 300 km/s) and non-rotating single stars at solar metallicity (Z=0.014) up to the onset of core collapse. We present the wind yields for the radioactive isotopes $^{26}$Al, $^{36}$Cl, and $^{41}$Ca, and the stable isotopes $^{19}$F and $^{20}$Ne. In relation to the stable isotopes, we find that only the most massive models, $geq$ 60M$_{odot}$ and $geq$ 40M$_{odot}$ give positive $^{19}$F and $^{20}$Ne yields, respectively, depending on the initial rotation rate. In relation to the radioactive isotopes, we find that the early Solar System abundances of $^{26}$Al and $^{41}$Ca can be matched with by models with initial masses $geq$40M$_{odot}$, while $^{36}$Cl is matched only by our most massive models, $geq$60M$_{odot}$. $^{60}$Fe is not significantly produced by any wind model, as required by the observations. Therefore, massive star winds are a favoured candidate for the origin of the very short-lived $^{26}$Al, $^{36}$Cl, and $^{41}$Ca in the early Solar System.
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Aluminium-26 is a short-lived radionuclide with a half-life of 0.72Myr, which is observed today in the Galaxy via gamma-ray spectroscopy and is inferred to have been present in the early Solar System via analysis of meteorites. Massive stars are considered the main contributors of Al26. Although most massive stars are found in binary systems, the effect, however, of binary interactions on the Al26 yields have not been investigated since Braun & Langer (1995). Here we aim to fill this gap. We have used the MESA stellar evolution code to compute massive (10Msun<=M<=80Msun), non-rotating, single and binary stars of solar metallicity (Z=0.014). We computed the wind yields for the single stars and for the binary systems where mass transfer plays a major role. Depending on the initial mass of the primary star and orbital period, the Al26 yield can either increase or decrease in a binary system. For binary systems with primary masses up to ~35-40Msun, the yield can increase significantly, especially at the lower mass-end, while above ~45Msun the yield becomes similar to the single star yield or even decreases. Our preliminary results show that compared to supernova explosions, the contribution of mass-loss in binary systems to the total Al26 abundance produced by a stellar population is minor. On the other hand, if massive star mass-loss is the origin of Al26 in the early Solar System, our results will have significant implications for the identification of the potential stellar, or stellar population, source.
Spectroscopic studies of Galactic O and B stars show that many stars with masses above 8 M$_{odot}$ are observed in the HR diagram just beyond the Main-Sequence (MS) band predicted by stellar models computed with a moderate overshooting. This may be an indication that the convective core sizes in stars in the upper part of the HR diagram are larger than predicted by these models. Combining stellar evolution models and spectroscopic parameters derived for a large sample of Galactic O and B stars, including brand new information about their projected rotational velocities, we reexamine the question of the convective core size in MS massive stars. We confirm that for stars more massive than about 8 M$_{odot}$, the convective core size at the end of the MS phase increases more rapidly with the mass than in models computed with a constant step overshoot chosen to reproduce the main sequence width in the low mass range (around 2 M$_{odot}$). This conclusion is valid for both the cases of non-rotating models and rotating models either with a moderate or a strong angular momentum transport. The increase of the convective core mass with the mass obtained from the TAMS position is, however, larger than the one deduced from the surface velocity drop for masses above about 15 M$_{odot}$. Although observations available at the moment cannot decide what is the best choice between the core sizes given by the TAMS and the velocity drop, we discuss different methods to get out of this dilemma. At the moment, comparisons with eclipsing binaries seem to favor the solution given by the velocity drop. While we confirm the need for larger convective cores at higher masses, we find tensions in-between different methods for stars more massive than 15 M$_{odot}$. The use of single-aged stellar populations (non-interacting binaries or stellar clusters) would be a great asset to resolve this tension.
Tidal dissipation in stars is one of the key physical mechanisms that drive the evolution of binary and multiple stars. As in the Earth oceans, it corresponds to the resonant excitation of their eigenmodes of oscillation and their damping. Therefore, it strongly depends on the internal structure, rotation, and dissipative mechanisms in each component. In this work, we present a local analytical modeling of tidal gravito-inertial waves excited in stellar convective and radiative regions respectively. This model allows us to understand in details the properties of the resonant tidal dissipation as a function of the excitation frequencies, the rotation, the stratification, and the viscous and thermal properties of the studied fluid regions. Then, the frequencies, height, width at half-height, and number of resonances as well as the non-resonant equilibrium tide are derived analytically in asymptotic regimes that are relevant in stellar interiors. Finally, we demonstrate how viscous dissipation of tidal waves leads to a strongly erratic orbital evolution in the case of a coplanar binary system. We characterize such a non-regular dynamics as a function of the height and width of resonances, which have been previously characterized thanks to our local fluid model.
The majority of massive stars live in binary or multiple systems and will interact during their lifetimes, which helps to explain the observed diversity of core-collapse supernovae. Donor stars in binary systems can lose most of their hydrogen-rich envelopes through mass transfer, which not only affects the surface properties, but also the core structure. However, most calculations of the core-collapse properties of massive stars rely on single-star models. We present a systematic study of the difference between the pre-supernova structures of single stars and stars of the same initial mass (11 - 21Msun) that have been stripped due to stable post-main sequence mass transfer at solar metallicity. We present the pre-supernova core composition with novel diagrams that give an intuitive representation of the isotope distribution. As shown in previous studies, at the edge of the carbon-oxygen core, the binary-stripped star models contain an extended gradient of carbon, oxygen, and neon. This layer originates from the receding of the convective helium core during core helium burning in binary-stripped stars, which does not occur in single-star models. We find that this same evolutionary phase leads to systematic differences in the final density and nuclear energy generation profiles. Binary-stripped star models have systematically higher total masses of carbon at the moment of core collapse compared to single star models, which likely results in systematically different supernova yields. In about half of our models, the silicon-burning and oxygen-rich layers merge after core silicon burning. We discuss the implications of our findings for the explodability, supernova observations, and nucleosynthesis from these stars. Our models will be publicly available and can be readily used as input for supernova simulations. [Abridged]
The first massive stars triggered the onset of chemical evolution by releasing the first metals (elements heavier than helium) in the Universe. The nature of these stars and how the early chemical enrichment took place is still largely unknown. Rotational-induced mixing in the stellar interior can impact the nucleosynthesis during the stellar life of massive stars and lead to stellar ejecta having various chemical compositions. We present low and zero-metallicity 20, 25 and 40 $M_{odot}$ stellar models with various initial rotation rates and assumptions for the nuclear reactions rates. With increasing initial rotation, the yields of light (from $sim$ C to Al) and trans-iron elements are boosted. The trans-iron elements (especially elements heavier than Ba) are significantly affected by the nuclear reaction uncertainties. The chemical composition of the observed CEMP (carbon-enhanced metal-poor) stars CS29528-028 and HE0336+0113 are consistent with the chemical composition of the material ejected by a fast rotating 40~$M_{odot}$ model.
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