The<i>R</i>-Process Alliance: Fourth Data Release from the Search for<i>R</i>-process-enhanced Stars in the Galactic Halo

Holmbeck, Erika M.; Hansen, Terese T.; Beers, Timothy C.; Placco, Vinicius M.; Whitten, Devin D.; Rasmussen, Kaitlin C.; Roederer, Ian U.; Ezzeddine, Rana; Sakari, Charli M.; Frebel, Anna; Drout, M. R.; Simon, Joshua D.; Thompson, I. B.; Bland‐Hawthorn, J.; Gibson, Brad K.; Grebel, Eva K.; Kordopatis, G.; Kunder, Andrea; Meléndez, Jorge; Navarro, Julio F.; Reid, Warren A.; Seabroke, G. M.; Steinmetz, Matthias; Watson, Fred; Wyse, Rosemary F. Ġ.

doi:10.3847/1538-4365/ab9c19

Cited by 89 publications

(63 citation statements)

References 97 publications

(101 reference statements)

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“…Such simplistic approaches should be testified by the future cosmological zoom-in simulations that resolve the UFDsized structures of MW-like galaxies. More measurements of stellar abundances in terms of both the number of stars and their accuracy will serve to refine the modelling of the enrichment history of the r-process elements in the MW (e.g., R-Process Alliance, Hansen et al 2018;Sakari et al 2018;Holmbeck et al 2020;Gudin et al 2021;GALAH, Buder et al 2021;Aguado et al 2021;Matsuno et al 2021;LAMOST, Chen et al 2021). In particular, more data are highly desired for UFDs and classical dwarf spheroidals as survivors from the early Galactic merging history.…”

Section: Discussionmentioning

confidence: 99%

Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies

Wanajo

Hirai

Prantzos

2021

Monthly Notices of the Royal Astronomical Society

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Recent progress of nucleosynthesis work as well as the discovery of a kilonova associated with the gravitational-wave source GW170817 indicates that neutron star mergers (NSM) can be a site of the r-process. Several studies of galactic chemical evolution, however, have pointed out inconsistencies between this idea and the observed stellar abundance signatures in the Milky Way: (a) the presence of Eu at low (halo) metallicity and (b) the descending trend of Eu/Fe at high (disc) metallicity. In this study, we explore the galactic chemical evolution of the Milky Way’s halo, disc and satellite dwarf galaxies. Particular attention is payed to the forms of delay-time distributions for both type Ia supernovae (SN Ia) and NSMs. The Galactic halo is modeled as an ensemble of independently evolving building-block galaxies with different masses. The single building blocks as well as the disc and satellite dwarfs are treated as well-mixed one-zone systems. Our results indicate that the aforementioned inconsistencies can be resolved and thus NSMs can be the unique r-process site in the Milky Way, provided that the delay-time distributions satisfy the following conditions: (i) a long delay (∼1 Gyr) for the appearance of the first SN Ia (or a slow early increase of its number) and (ii) an additional early component providing $\gtrsim 50{{\ \rm per\ cent}}$ of all NSMs with a delay of ∼0.1 Gyr. In our model, r-process-enhanced and r-process-deficient stars in the halo appear to have originated from ultra-faint dwarf-sized and massive building blocks, respectively. Our results also imply that the natal kicks of binary neutron stars have a little impact on the evolution of Eu in the disc.

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Section: Discussionmentioning

confidence: 99%

Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies

Wanajo

Hirai

Prantzos

2021

Monthly Notices of the Royal Astronomical Society

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“…For the mapping of RPE stars onto our DTGs, carried out in Section 7, we have adopted the recent compilation of r-I and r-II stars from Gudin et al (2020). The majority of these objects come from the R-Process Alliance data releases (Hansen et al 2018;Sakari et al 2018;Ezzeddine et al 2020;Holmbeck et al 2020), complemented with additional data from JINAbase (Abohalima & Frebel 2018). These stars are all metal-poor ([Fe/H] < −1.0) and at least moderately enriched in rprocess elements ([Eu/Fe] > +0.3; [Ba/Eu] < 0.0).…”

Section: The Rpe Stars Samplementioning

confidence: 99%

Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys

Limberg¹,

Rossi²,

Perottoni³

et al. 2021

ApJ

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We analyze the dynamical properties of ∼1500 very metal-poor (VMP; [Fe/H] −2.0) halo stars, based primarily on medium-resolution spectroscopic data from the HK and Hamburg/ESO surveys. These data, collected over the past thirty years, are supplemented by a number of calibration stars and other small samples, along with astrometric information from Gaia DR2. We apply a clustering algorithm to the 4-D energy-action space of the sample, and identify a set of 38 Dynamically Tagged Groups (DTGs), containing between 5 and 30 member stars. Many of these DTGs can be associated with previously known prominent substructures such as Gaia-Sausage/Enceladus (GSE), Sequoia, the Helmi Stream (HStr), and Thamnos. Others are associated with previously identified smaller dynamical groups of stars and streams. We identify 10 new DTGs as well, many of which have strongly retrograde orbits. We also investigate possible connections between our DTGs and ∼300 individual r-processenhanced (RPE) stars from a recent literature compilation. We find that several of these objects have similar dynamical properties to GSE (5), the HStr (4), Sequoia (1), and Rg5 (1), indicating that their progenitors might have been important sources of RPE stars in the Galaxy. Additionally, a number of our newly identified DTGs are shown to be associated with at least two RPE stars each (DTG-2: 3, DTG-7: 2; DTG-27: 2). Taken as a whole, these results are consistent with ultra-faint and/or dwarf spheroidal galaxies as birth environments in which r-process nucleosynthesis took place, and then were disrupted by the Milky Way.

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“…Figure 4 shows examples of all of these syntheses. The errors for these abundance estimates are 0.20 dex for Ba and Eu and 0.30 dex for C, based on the systematic errors arising from errors in stellar parameters as described in Holmbeck et al (2020) for spectra of similar resolution, S/N, and stellar parameters. To account for isotopic differences in these syntheses we considered the following isotopes: 12 C, 13 C, 134 Ba, 135 Ba, 136 Ba, 137 Ba, 138 Ba, 151 Eu, and 153 Eu.…”

Section: Synthesis Measurementsmentioning

confidence: 99%

Metal-Poor Stars Observed with the Southern African Large Telescope II. An Extended Sample

Zepeda,

Rasmussen,

Beers

et al. 2021

Preprint

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We present results from high-resolution (R ∼ 40, 000) spectroscopic observations of over 200 metalpoor stars, mostly selected from the RAVE survey, using the Southern African Large Telescope. We were able to derive stellar parameters for a total of 108 stars; an additional sample of 50 stars from this same effort was previously reported on by Rasmussen et al.. Among our newly reported observations, we identify 84 very metal-poor (VMP; [Fe/H] < −2.0, 53 newly identified) stars and 3 extremely metalpoor (EMP; [Fe/H] < −3.0, 1 newly identified) stars. The elemental abundances were measured for carbon, as well as several other 𝛼-elements (Mg, Ca, Sc, Ti), iron-peak elements (Mn, Co, Ni, Zn), and neutron-capture elements (Sr, Ba, Eu). Based on these measurements, the stars are classified by their carbon and neutron-capture abundances into carbon-enhanced metal-poor (CEMP; [C/Fe] > +0.70), CEMP sub-classes, and by the level of their 𝑟-process abundances. A total of 17 are classified as CEMP stars. There are 11 CEMP-𝑟 stars (8 newly identified), 1 CEMP-𝑠 star (newly identified), 2 possible CEMP-𝑖 stars (1 newly identified), and 3 CEMP-no stars (all newly identified) in this work. We found 11 stars (8 newly identified) that are strongly enhanced in 𝑟-process elements (𝑟-II; [Eu/Fe] > +0.70), 38 stars (31 newly identified) that are moderately enhanced in 𝑟-process elements (𝑟-I; +0.30 < [Eu/Fe] ≤ +0.70), and 1 newly identified limited-𝑟 star.

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TheR-Process Alliance: Fourth Data Release from the Search forR-process-enhanced Stars in the Galactic Halo

Cited by 89 publications

References 97 publications

Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies

Neutron star mergers as the astrophysical site of the r-process in the Milky Way and its satellite galaxies

Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys

Metal-Poor Stars Observed with the Southern African Large Telescope II. An Extended Sample

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