The r-process in Magnetorotational Supernovae

Abstract

One of the hottest open issues involving the evolution of r-process elements is fast enrichment in the early Universe. Clear evidence for the chemical enrichment of r-process elements is seen in the stellar abundances of extremely metal poor stars in the Galactic halo. However, small-mass galaxies are the ideal testbed for studying the evolutionary features of r-process enrichment given the potential rarity of production events yielding heavy r-process elements. Their occurrences become countable and thus an enrichment path due to each event can be found in the stellar abundances. We examine the chemical feature of Eu abundance at an early stage of $[Fe/H]\lesssim -2$ in the Draco and Sculptor dwarf spheroidal (dSph) galaxies. Accordingly, we constrain the properties of the Eu production in the early dSphs. We find that the Draco dSph experienced a few Eu production events, whereas Eu enrichment took place more continuously in the Sculptor dSph due to its larger stellar mass. The event rate of Eu production is estimated to be about one per $100$-$200$ core-collapse supernovae, and a Eu mass of $\sim (1-2)\times 10^{-5}$\ms per single event is deduced by associating this frequency with the observed plateau value of $[Eu/H]\sim -1.3$ for $[Fe/H]\gtrsim -2$. The observed plateau implies that early Eu enrichment ceases at $[Fe/H]\approx -2$. Such a selective operation only in low-metallicity stars supports magnetorotational supernovae, which require very fast rotation, as the site of early Eu production. We show that the Eu yields deduced from chemical evolution agree well with the nucleosynthesis results from corresponding supernovae models.

5 pages, 3 figures, published in ApJL 811:L10 (2015); Title is changed

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• Nucleosynthesis in Magnetically Driven Jets from Collapsars
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• Enrichment history of r-process elements shaped by a merger of neutron star pairs
• Chemical Signatures of the First Supernovae in the Sculptor Dwarf Spheroidal Galaxy
• A high-entropy wind r-process study based on nuclear-structure quantities from the new finite-range droplet model FRDM(2012)
• A Search for New Galactic Magnetars in Archival Chandra and XMM-Newton Observations
• Chemical Feature of Eu abundance in the Draco dwarf spheroidal galaxy

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• The R-Process Alliance: First Release from the Northern Search for r-Process Enhanced Metal-Poor Stars in the Galactic Halo
• Kinematics of Highly R-Process-Enhanced Field Stars: Evidence for an Accretion Origin and Detection of Several Groups from Disrupted Satellites
• RAVE J203843.2-002333: The first highly r-process-enhanced star identified in the RAVE survey
• The Populations of Carina. II. Chemical Enrichment
• The r-Process Pattern of a Bright, Highly r-Process-Enhanced, Metal-Poor Halo Star at [Fe/H] ~ -2
• Enrichment in r-process elements from multiple distinct events in the early Draco dwarf spheroidal galaxy
• Early chemo-dynamical evolution of dwarf galaxies deduced from enrichment of r-process elements
• Neutron Star Mergers Are the Dominant Source of the r-process in the Early Evolution of Dwarf Galaxies
• On the R-Process Enrichment of Dwarf Spheroidal Galaxies
• The Pristine survey -- XII: Gemini-GRACES chemo-dynamical study of newly discovered extremely metal-poor stars in the Galaxy
• On the neutron-capture elements across the Galactic thin disk using Cepheids
• Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies
• Impact of the first-forbidden $\beta$ decay on the production of $A\sim 195$ r-process peak
• Neutron-capture elements in dwarf galaxies I: Chemical clocks & the short timescale of the r-process
• Early chemical evolution of Zn driven by magnetorotational supernovae and the pathway to the solar Zn composition
• Magnetically-Driven Neutron-Rich Ejecta Unleashed: Global 3D Neutrino-General Relativistic Magnetohydrodynamic Simulations of Collapsars Probe the Conditions for r-process Nucleosynthesis
• Chemical enrichment by collapsars as the origin of the unusually high [Ba/Fe] in a massive star cluster of the dwarf galaxy NGC 1569
• Radiative neutron capture reaction rates for r-process nucleosynthesis
• Detailed Abundance Determination of Metal-Poor Stars with X-Shooter I. Unusual Chemistry in Halo Stars
• Two Sites of r-Process Production Assessed on the Basis of the Age-tagged Abundances of Solar Twins