Evolution of heavy-element abundances as a constraint on sites for neutron-capture nucleosynthesis

Mathews, Grant J.; Bazán, G.; Cowan, J. J.

doi:10.1086/171383

Cited by 150 publications

(143 citation statements)

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“…In the Sun roughly 80% of the Y and Ba is a consequence of s-process fusion (Wallerstein et al 1997). The weak and strong s-process may occur in massive to intermediate-mass to low-mass stars, while high-mass stars may synthesize r-process elements (Mathews, Bazan, & Cowan 1992). Although the source of these elements in metal-poor stars is largely unknown, McWilliam (1997McWilliam ( , 1998 suggests that the r-process may be a significant producer of Ba in low-metallicity stars.…”

Section: Sodiummentioning

confidence: 99%

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Stephens

Boesgaard

2002

The Astronomical Journal

146

182

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There are stars in the halo of the Galaxy whose orbital properties are distinctly different from the majority of the halo population. One suggestion to account for these kinematically peculiar stars is that they have been gravitationally subsumed by the Milky Way through the breakup of nearby dwarf galaxies. One test of this hypothesis lies in determining the chemical composition of the deviant halo stars relative to that of normal ('' native '') halo field stars. The possibly accreted stars are predicted to have different chemical enrichments due to a slower rate of star formation in nearby low-mass spheroidal or irregular galaxies. We have obtained echelle spectra of metal-poor halo dwarfs with unusual orbital properties: from the outer halo, from the '' high '' halo, and on retrograde orbits. Our spectra are at high spectral resolution (35,000-48,000) and high signal-to-noise ratios (median value 140), primarily from the Keck I 10 m telescope with HIRES (53 stars), but also from the echelle spectrometer of the KPNO Mayall 4 m Telescope (three stars). The spectra cover a large spectral range: $4000-6800 Å . The strengths of approximately 9000 lines have been measured to determine the stellar parameters (T eff , log g, [Fe/H], and ) and the abundances of 10 elements, including Na, -fusion products (Mg, Si, Ca, Ti), iron peak elements (Cr, Fe, Ni), and neutron capture elements (Y, Ba). A model atmosphere was computed for each star, which was used to determine the composition under the assumption of LTE. The comparison of the abundances with the kinematic properties revealed no special trends, except that the ratio of the mean of the -fusion elements to Fe is weakly correlated with stellar apogalactica in the sense that the outermost stars have lower ratios of [ /Fe] than those with smaller apogalactica. The hallmark of an accreted halo star is presumed to be a deficiency (compared with normal stars) of the -elements (e.g., O, Mg, Si, Ca, Ti) with respect to Fe, a consequence of sporadic bursts of star formation within the dwarf galaxies. However [Fe/H]. The kinematically peculiar stars in our sample must have had their origins in localized star-forming regions far removed from the Galactic center. They do not carry the chemical signature of an accreted population. It seems clear that the chemical enrichment in our sample comes primarily from Type II supernovae with only a small component from Type Ia supernovae. Our stars would have formed at most $1 Gyr after the beginning of a star formation episode in the remote halo. The general conclusion extracted from these data is that the formation of the nascent Milky Way was not dominated by the late accretion of dwarf galaxies like the ones that currently orbit the Galaxy. However, the assimilation of fragments early in the evolution of the Galaxy is a natural by-product of hierarchical models of structure formation and can explain many properties of the halo population.

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Section: Sodiummentioning

confidence: 99%

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Stephens

Boesgaard

2002

The Astronomical Journal

146

182

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“…This is in part due to their short delays following star formation, which allows the earliest generations of metal-poor stars in our Galaxy (e.g. Mathews et al 1992, Sneden et al 2008), or satellite dwarf galaxies (e.g. Roederer 2016), to be polluted with r-process elements prior to significant iron en-E-mail: adv2110@columbia.edu richment.…”

Section: Introductionmentioning

confidence: 99%

Neutrino-heated winds from millisecond protomagnetars as sources of the weak r-process

Vlasov

Metzger

Lippuner

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We explore heavy element nucleosynthesis in neutrino-driven winds from rapidly-rotating, strongly magnetized proto-neutron stars ("millisecond proto-magnetars") for which the magnetic dipole is aligned with the rotation axis, and the field is assumed to be a static force-free configuration. We process the proto-magnetar wind trajectories calculated by Vlasov et al. (2014) through the r-process nuclear reaction network SkyNet using contemporary models for the evolution of the wind electron fraction during the proto-neutron star cooling phase. Although we do not find a successful second or third peak r-process for any rotation period P, we show that proto-magnetars with P ∼ 1 − 5 ms produce heavy element abundance distributions that extend to higher nuclear mass number than from otherwise equivalent spherical winds (with the mass fractions of some elements enhanced by factors of ∼ > 100 − 1000). The heaviest elements are synthesized by outflows emerging along flux tubes which graze the closed zone and pass near the equatorial plane outside the light cylinder. Due to dependence of the nucleosynthesis pattern on the magnetic field strength and rotation rate of the proto-neutron star, natural variations in these quantities between core collapse events could contribute to the observed diversity of the abundances of weak r-process nuclei in metal-poor stars. Further diversity, including possibly even a successful third-peak r-process, could be achieved for misaligned rotators with non-zero magnetic inclination with respect to the rotation axis. If proto-magnetars are central engines for GRBs, their relativistic jets should contain a high mass fraction of heavy nuclei of characteristic mass numberĀ ≈ 100, providing a possible source for ultra-high energy cosmic rays comprised of heavy nuclei with an energy spectrum that extends beyond the nominal GZK cut-off for protons or iron nuclei.

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“…The site or sites of the r-process are not known, although suggestions include the ν-driven wind of Type II SNe (e.g., Woosly and Hoffman, 1992; Woosly et al, 1994) and the mergers of neutron stars (e.g., Lattimer and Schramm, 1974; Rosswog et al, 2000). Particular attention to the Galactic evolution of elements produced by neutron-capture nucleosynthesis was given by Mathews et al, (1992), Pagel and Tautvaisiene (1997), and more recently by Travaglio et al (1999). These authors adopted the standard approach to Galactic chemical evolution, assuming that stars form from a chemically homogeneous medium at a continuous rate.…”

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confidence: 99%

The Yields of r-Process Elements and Chemical Evolution of the Galaxy

Chen

Zhang

Chen

et al. 2006

Astrophys Space Sci

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The supernova yields of r-process elements are obtained as a function of the mass of their progenitor stars from the abundance patterns of extremely metalpoor stars on the left-side [Ba/Mg]-[Mg/H] boundary with a procedure proposed by Tsujimoto and Shigeyama. The ejected masses of r-process elements associated with stars of progenitor mass M ms ≤ 18M ⊙ are infertile sources and the SNe II with 20M ⊙ ≤ M ms ≤ 40M ⊙ are the dominant source of r-process nucleosynthesis in the Galaxy. The ratio of these stars 20M ⊙ ≤ M ms ≤ 40M ⊙ with compared to the all massive stars is about ∼18%. In this paper, we present a simple model that describes a star's [r/Fe] in terms of the nucleosynthesis yields of r-process elements and the number of SN II explosions. Combined the r-process yields obtained by our procedure with the scatter model of the Galactic halo, the observed abundance patterns of the metal-poor stars can be well reproduced.

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Evolution of heavy-element abundances as a constraint on sites for neutron-capture nucleosynthesis

Cited by 150 publications

References 0 publications

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Abundances from High-Resolution Spectra of Kinematically Interesting Halo Stars

Neutrino-heated winds from millisecond protomagnetars as sources of the weak r-process

The Yields of r-Process Elements and Chemical Evolution of the Galaxy

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