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 »
A promising formation channel for symbiotic X-ray binaries: cases of IGR J17329−2731 and 4U 1700+24
Recent observations demonstrate that the symbiotic X-ray binary (SyXB) IGR J17329−2731 contains a highly magnetized neutron star (NS), which accretes matter through the wind from its giant star companion, and suggest that 4U 1700+24 may also have a highly magnetized NS. Accretion-induced collapse (AIC) from oxygen–neon–magnesium white dwarf (ONeMg WD) + red giant (RG) star binaries is one promising channel to form these SyXBs, while other long standing formation channels have difficulties to produce these SyXBs. By considering non-magnetic and magnetic ONeMg WDs, I investigate the evolution of ONeMg WD + RG binaries with the mesa stellar evolution code for producing SyXBs with non-magnetic or magnetized NSs. In the pre-AIC evolution with magnetic confinement, the mass accumulation efficiency of the accreting WD is increased at low-mass transfer rate compared with the non-magnetic case. The newborn NSs formed via AIC of highly magnetized WDs could inherit the large magnetic field through conservation of magnetic flux, and the systems could have a long age compatible with that of the red giant companions. These young and highly magnetized NSs could accrete matters from the stellar wind of the giant companions to that shine as those observed SyXBs, and could preserve their high magnetic more »
- Publication Date:
- NSF-PAR ID:
- 10387604
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 519
- Issue:
- 1
- Page Range or eLocation-ID:
- p. 1327-1335
- ISSN:
- 0035-8711
- Publisher:
- Oxford University Press
- Sponsoring Org:
- National Science Foundation
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