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Very massive star winds as sources of the short-lived radioactive isotope 26 Al
Context. The 26 Al short-lived radioactive nuclide is the source of the observed galactic diffuse γ -ray emission at 1.8 MeV. While different sources of 26 Al have been explored, such as asymptotic giant branch stars, massive stellar winds, and supernovae, the contribution of very massive stars has not been studied so far. Aims. We study the contribution of the stellar wind of very massive stars, here, stars with initial masses between 150 and 300 M ⊙ , to the enrichment in 26 Al of the galactic interstellar medium. Methods. We studied the production of 26 Al by studying rotating and non-rotating very massive stellar models with initial masses between 150 and 300 M ⊙ for metallicities Z  = 0.006, 0.014, and 0.020. We compared this result to a simple Milky Way model and took the metallicity and the star formation rate gradients into account. Results. We obtain that very massive stars in the Z  = 0.006 − 0.020 metallicity range might be very significant contributors to the 26 Al enrichment of the interstellar medium. Typically, the contribution of the winds of massive stars to the total quantity of 26 Al in the Galaxy increases by 150% when very massive stars are considered. Conclusions. more »
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Award ID(s):
Publication Date:
NSF-PAR ID:
10358357
Journal Name:
Astronomy & Astrophysics
Volume:
664
Page Range or eLocation-ID:
A181
ISSN:
0004-6361
We present a grid of stellar models at supersolar 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 disc. A modest increase of 43 per cent (= 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 supersolar 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 supersolar models to the Westerlund 1 (Wd1) massive young cluster. A synthetic cluster combining rotating and non-rotating models with an age spread between log10(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 $\log _{10}(L/\mathit {\mathrm{ L}}_{\odot })$ = 5–5.5. The quantitative agreement is imperfect and wemore »
4. ABSTRACT We test the hypothesis that the observed first-peak (Sr, Y, Zr) and second-peak (Ba) s-process elemental abundances in low-metallicity Milky Way stars, and the abundances of the elements Mo and Ru, can be explained by a pervasive r-process contribution originating in neutrino-driven winds from highly magnetic and rapidly rotating proto-neutron stars (proto-NSs). We construct chemical evolution models that incorporate recent calculations of proto-NS yields in addition to contributions from asymptotic giant branch stars, Type Ia supernovae, and two alternative sets of yields for massive star winds and core-collapse supernovae. For non-rotating massive star yields from either set, models without proto-NS winds underpredict the observed s-process peak abundances by 0.3–$1\, \text{dex}$ at low metallicity, and they severely underpredict Mo and Ru at all metallicities. Models incorporating wind yields from proto-NSs with spin periods P ∼ 2–$5\, \text{ms}$ fit the observed trends for all these elements well. Alternatively, models omitting proto-NS winds but adopting yields of rapidly rotating massive stars, with vrot between 150 and $300\, \text{km}\, \text{s}^{-1}$, can explain the observed abundance levels reasonably well for [Fe/H] < −2. These models overpredict [Sr/Fe] and [Mo/Fe] at higher metallicities, but with a tuned dependence of vrot on stellar metallicity they mightmore »