The r-process Pattern of a Bright, Highly r-process-enhanced Metal-poor Halo Star at [Fe/H] ∼ −2

Sakari, Charli M.; Placco, Vinicius M.; Hansen, Terese T.; Holmbeck, Erika M.; Beers, Timothy C.; Frebel, Anna; Roederer, Ian U.; Venn, Kim A.; Wallerstein, George; Davis, C.; Farrell, E. M.; Yong, David

doi:10.3847/2041-8213/aaa9b4

Cited by 46 publications

(48 citation statements)

References 53 publications

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“…A newly revealed example is the retrograde halo star RAVE J153830. (Sakari et al 2018). Detailed modeling of the actinide elements (Th, U) with respect to the other heavy elements supports the idea of this star being ancient, albeit with systematic uncertainties of several Gyr.…”

Section: Prospects For Identifying the Oldest Starsmentioning

confidence: 53%

Where are the most ancient stars in the Milky Way?

El-Badry

Bland-Hawthorn

Wetzel

et al. 2018

Monthly Notices of the Royal Astronomical Society

122

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The oldest stars in the Milky Way (MW) bear imprints of the Galaxy's early assembly history. We use FIRE cosmological zoom-in simulations of three MW-mass disk galaxies to study the spatial distribution, chemistry, and kinematics of the oldest surviving stars (z form 5) in MW-like galaxies. We predict the oldest stars to be less centrally concentrated at z = 0 than stars formed at later times as a result of two processes. First, the majority of the oldest stars are not formed in situ but are accreted during hierarchical assembly. These ex situ stars are deposited on dispersion-supported, halolike orbits but dominate over old stars formed in situ in the solar neighborhood, and in some simulations, even in the galactic center. Secondly, old stars formed in situ are driven outwards by bursty star formation and energetic feedback processes that create a time-varying gravitational potential at z 2, similar to the process that creates dark matter cores and expands stellar orbits in bursty dwarf galaxies. The total fraction of stars that are ancient is more than an order of magnitude higher for sight lines away from the bulge and inner halo than for inward-looking sight lines. Although the task of identifying specific stars as ancient remains challenging, we anticipate that million-star spectral surveys and photometric surveys targeting metal-poor stars already include hundreds of stars formed before z = 5. We predict most of these targets to have higher metallicity (−3 < [Fe/H] < −2) than the most extreme metal-poor stars.

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Section: Prospects For Identifying the Oldest Starsmentioning

confidence: 53%

Where are the most ancient stars in the Milky Way?

El-Badry

Bland-Hawthorn

Wetzel

et al. 2018

Monthly Notices of the Royal Astronomical Society

122

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“…Sneden et al (2003) first showed that the abundances of CS 22892-052, an r-II star, was similar within 0.2 − 0.3 dex to the solar r-process pattern between the second and third peak. Since then, many studies found additional r-process enhanced stars that also show this pattern with similar precisions (Roederer et al 2009a;Cowan et al 2011;Roederer et al 2012b;Mashonkina et al 2014;Ji et al 2016b;Placco et al 2017;Holmbeck et al 2018;Sakari et al 2018). This pattern has also been found in dwarf galaxy stars, such as in Reticulum II (Ji et al 2016b;Ji & Frebel 2018).…”

Section: R-process Enhanced Starsmentioning

confidence: 59%

Neutron Star Mergers Might Not Be the Only Source of r-process Elements in the Milky Way

Côté

Eichler

Arcones

et al. 2019

ApJ

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226

192

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Probing the origin of r-process elements in the universe represents a multi-disciplinary challenge. We review the observational evidence that probe the properties of r-process sites, and address them using galactic chemical evolution simulations, binary population synthesis models, and nucleosynthesis calculations. Our motivation is to define which astrophysical sites have significantly contributed to the total mass of r-process elements present in our Galaxy. We found discrepancies with the neutron star (NS-NS) merger scenario. Assuming they are the only site, the decreasing trend of [Eu/Fe] at [Fe/H] > −1 in the disk of the Milky Way cannot be reproduced while accounting for the delaytime distribution (DTD) of coalescence times (∝ t −1 ) derived from short gamma-ray bursts and population synthesis models. Steeper DTD functions (∝ t −1.5 ) or power laws combined with a strong burst of mergers before the onset of Type Ia supernovae can reproduce the [Eu/Fe] trend, but this scenario is inconsistent with the similar fraction of short gamma-ray bursts and Type Ia supernovae occurring in early-type galaxies, and reduces the probability of detecting GW170817 in an early-type galaxy. One solution is to assume an extra production site of Eu that would be active in the early universe, but would fade away with increasing metallicity. If this is correct, this extra site could be responsible for roughly 50 % of the Eu production in the early universe, before the onset of Type Ia supernovae. Rare classes of supernovae could be this additional r-process source, but hydrodynamic simulations still need to ensure the conditions for a robust r-process pattern.

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“…It is also worth noting that the stellar mass of Ret II is (2.6±0.2)×10 3 M e (Bechtol et al 2015), that of Tuc III is (0.8±0.1)×10 3 M e (Drlica-Wagner et al 2015), and that of the Tuc III stream is 3.8×10 3 M e (Shipp et al 2018), so many possible dilution scenarios are plausible. Sakari et al (2018b) show that r-process enhanced stars in the Milky Way halo at a range of metallicities have nearly identical r-process patterns, matching the solar system r-process pattern, regardless of the level of r-process enhancement. Hansen et al (2017) also found this to be true for the r-process enhanced stars detected in classical and ultra-faint dwarf galaxies.…”

Section: The R-process Enhancement Eventmentioning

confidence: 74%

Chemical Abundance Analysis of Tucana III, the Second r-process Enhanced Ultra-faint Dwarf Galaxy*

Marshall¹,

Hansen²,

Simon³

et al. 2019

ApJ

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We present a chemical abundance analysis of four additional confirmed member stars of Tucana III, a Milky Way satellite galaxy candidate in the process of being tidally disrupted as it is accreted by the Galaxy. Two of these stars are centrally located in the core of the galaxy while the other two stars are located in the eastern and western tidal tails. The four stars have chemical abundance patterns consistent with the one previously studied star in Tucana III: they are moderately enhanced in r-process elements, i.e., they have [ ] á ñ » + Eu Fe 0.4 dex.

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The r-process Pattern of a Bright, Highly r-process-enhanced Metal-poor Halo Star at [Fe/H] ∼ −2

Cited by 46 publications

References 53 publications

Where are the most ancient stars in the Milky Way?

Where are the most ancient stars in the Milky Way?

Neutron Star Mergers Might Not Be the Only Source of r-process Elements in the Milky Way

Chemical Abundance Analysis of Tucana III, the Second r-process Enhanced Ultra-faint Dwarf Galaxy*

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