scholarly journals R-process-rich Stellar Streams in the Milky Way*

2021 ◽  
Vol 912 (1) ◽  
pp. 52
Author(s):  
Maude Gull ◽  
Anna Frebel ◽  
Karina Hinojosa ◽  
Ian U. Roederer ◽  
Alexander P. Ji ◽  
...  
Keyword(s):  
Milky Way ◽  
Stellar Streams ◽  
R Process

scholarly journals The AMBRE Project: r-process elements in the Milky Way thin and thick discs

2018 ◽  
Vol 619 ◽  
pp. A143 ◽  
Author(s):  
G. Guiglion ◽  
P. de Laverny ◽  
A. Recio-Blanco ◽  
N. Prantzos
Keyword(s):  
Chemical Evolution ◽  
Milky Way ◽  
Element Abundances ◽  
Thick Disc ◽  
Thin Disc ◽  
Solar Metallicity ◽  
R Process ◽  
Process Elements ◽  
Process Element ◽  
The Eu

Context. The chemical evolution of neutron capture elements in the Milky Way disc is still a matter of debate. There is a lack of statistically significant catalogues of such element abundances, especially those of the r-process. Aims. We aim to understand the chemical evolution of r-process elements in Milky Way disc. We focus on three pure r-process elements Eu, Gd, and Dy. We also consider a pure s-process element, Ba, in order to disentangle the different nucleosynthesis processes. Methods. We take advantage of high-resolution FEROS, HARPS, and UVES spectra from the ESO archive in order to perform a homogeneous analysis on 6500 FGK Milky Way stars. The chemical analysis is performed thanks to the automatic optimization pipeline GAUGUIN. We present abundances of Ba (5057 stars), Eu (6268 stars), Gd (5431 stars), and Dy (5479 stars). Based on the [α/Fe] ratio determined previously by the AMBRE Project, we chemically characterize the thin and the thick discs, and a metal-rich α-rich population. Results. First, we find that the [Eu/Fe] ratio follows a continuous sequence from the thin disc to the thick disc as a function of the metallicity. Second, in thick disc stars, the [Eu/Ba] ratio is found to be constant, while the [Gd/Ba] and [Dy/Ba] ratios decrease as a function of the metallicity. These observations clearly indicate a different nucleosynthesis history in the thick disc between Eu and Gd–Dy. The [r/Fe] ratio in the thin disc is roughly around +0.1 dex at solar metallicity, which is not the case for Ba. We also find that the α-rich metal-rich stars are also enriched in r-process elements (like thick disc stars), but their [Ba/Fe] is very different from thick disc stars. Finally, we find that the [r/α] ratio tends to decrease with metallicity, indicating that supernovae of different properties probably contribute differently to the synthesis of r-process elements and α-elements. Conclusions. We provide average abundance trends for [Ba/Fe] and [Eu/Fe] with rather small dispersions, and for the first time for [Gd/Fe] and [Dy/Fe]. This data may help to constrain chemical evolution models of Milky Way r- and s-process elements and the yields of massive stars. We emphasize that including yields of neutron-star or black hole mergers is now crucial if we want to quantitatively compare observations to Galactic chemical evolution models.

scholarly journals Chemical Abundances of Seven Outer Halo M31 Globular Clusters from the Pan-Andromeda Archaeological Survey

2016 ◽  
Vol 11 (S321) ◽  
pp. 10-12
Author(s):  
Charli M. Sakari
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Large Magellanic Cloud ◽  
Archaeological Survey ◽  
Chemical Abundances ◽  
Light Spectra ◽  
Sigma Level ◽  
Stellar Streams ◽  
Detailed Chemical

AbstractObservations of stellar streams in M31’s outer halo suggest that M31 is actively accreting several dwarf galaxies and their globular clusters (GCs). Detailed abundances can chemically link clusters to their birth environments, establishing whether or not a GC has been accreted from a satellite dwarf galaxy. This talk presents the detailed chemical abundances of seven M31 outer halo GCs (with projected distances from M31 greater than 30 kpc), as derived from high-resolution integrated-light spectra taken with the Hobby Eberly Telescope. Five of these clusters were recently discovered in the Pan-Andromeda Archaeological Survey (PAndAS)—this talk presents the first determinations of integrated Fe, Na, Mg, Ca, Ti, Ni, Ba, and Eu abundances for these clusters. Four of the target clusters (PA06, PA53, PA54, and PA56) are metal-poor ([Fe/H] < -1.5), α-enhanced (though they are possibly less alpha-enhanced than Milky Way stars at the 1 sigma level), and show signs of star-to-star Na and Mg variations. The other three GCs (H10, H23, and PA17) are more metal-rich, with metallicities ranging from [Fe/H] = -1.4 to -0.9. While H23 is chemically similar to Milky Way field stars, Milky Way GCs, and other M31 clusters, H10 and PA17 have moderately-low [Ca/Fe], compared to Milky Way field stars and clusters. Additionally, PA17’s high [Mg/Ca] and [Ba/Eu] ratios are distinct from Milky Way stars, and are in better agreement with the stars and clusters in the Large Magellanic Cloud (LMC). None of the clusters studied here can be conclusively linked to any of the identified streams from PAndAS; however, based on their locations, kinematics, metallicities, and detailed abundances, the most metal-rich PAndAS clusters H23 and PA17 may be associated with the progenitor of the Giant Stellar Stream, H10 may be associated with the SW Cloud, and PA53 and PA56 may be associated with the Eastern Cloud.

scholarly journals The contribution from rotating massive stars to the enrichment in Sr and Ba of the Milky Way

2019 ◽  
Author(s):  
F Rizzuti ◽  
G Cescutti ◽  
F Matteucci ◽  
A Chieffi ◽  
R Hirschi ◽  
...  
Keyword(s):  
Neutron Capture ◽  
Milky Way ◽  
Massive Stars ◽  
Rotational Velocity ◽  
Stellar Rotation ◽  
Deep Impact ◽  
Low Metallicity ◽  
Group Rotation ◽  
R Process ◽  
Chemical Evolution Model

Abstract Most neutron capture elements have a double production by r- and s-processes, but the question of production sites is complex and still open. Recent studies show that including stellar rotation can have a deep impact on nucleosynthesis. We studied the evolution of Sr and Ba in the Milky Way. A chemical evolution model was employed to reproduce the Galactic enrichment. We tested two different nucleosynthesis prescriptions for s-process in massive stars, adopted from the Geneva group and the Rome group. Rotation was taken into account, studying the effects of stars without rotation or rotating with different velocities. We also tested different production sites for the r-process: magneto rotational driven supernovae and neutron star mergers. The evolution of the abundances of Sr and Ba is well reproduced. The comparison with the the most recent observations shows that stellar rotation is a good assumption, but excessive velocities result in overproduction of these elements. In particular, the predicted evolution of the [Sr/Ba] ratio at low metallicity does not explain the data at best if rotation is not included. Adopting different rotational velocities for different stellar mass and metallicity better explains the observed trends. Despite the differences between the two sets of adopted stellar models, both show a better agreement with the data assuming an increase of rotational velocity toward low metallicity. Assuming different r-process sources does not alter this conclusion.

scholarly journals Extended stellar systems in the solar neighborhood

2019 ◽  
Vol 622 ◽  
pp. L13 ◽  
Author(s):  
Stefan Meingast ◽  
João Alves ◽  
Verena Fürnkranz
Keyword(s):  
Wavelet Decomposition ◽  
Stellar Population ◽  
Main Sequence ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Galactic Disk ◽  
Mass Function ◽  
Solar Neighborhood ◽  
Giant Stars ◽  
Stellar Streams

We report the discovery of a large, dynamically cold, coeval stellar stream that is currently traversing the immediate solar neighborhood at a distance of only 100 pc. The structure was identified in a wavelet decomposition of the 3D velocity space of all stars within 300 pc of the Sun. Its members form a highly elongated structure with a length of at least 400 pc, while its vertical extent measures only about 50 pc. Stars in the stream are not isotropically distributed but instead form two parallel lanes with individual local overdensities, that may correspond to a remnant core of a tidally disrupted cluster or OB association. Its members follow a very well-defined main sequence in the observational Hertzsprung–Russel diagram and also show a remarkably low 3D velocity dispersion of only 1.3 km s−1. These findings strongly suggest a common origin as a single coeval stellar population. An extrapolation of the present-day mass function indicates a total mass of at least 2000 M⊙, making it larger than most currently known clusters or associations in the solar neighborhood. We estimated the age of the stream to be around 1 Gyr based on a comparison with a set of isochrones and giant stars in our member selection and find a mean metallicity of [Fe/H] = −0.04. This structure may very well represent the Galactic disk counterpart to the prominent stellar streams observed in the Milky Way halo. As such, it constitutes a new valuable probe to constrain the Galaxy’s mass distribution.

Stellar Populations of the Outer Milky-Way Halo

2017 ◽  
Vol 13 (S334) ◽  
pp. 29-33
Author(s):  
Baslio Santiago ◽  
Elmer Luque ◽  
Adriano Pieres ◽  
Anna Bárbara Queiroz
Keyword(s):  
Galaxy Evolution ◽  
Galaxy Formation ◽  
Milky Way ◽  
Galactic Halo ◽  
Dwarf Galaxy ◽  
Building Blocks ◽  
Early Stages ◽  
Dark Energy Survey ◽  
Stellar Streams ◽  
The Galaxy

AbstractThe stellar spheroidal components of the Milky-Way contain the oldest and most metal poor of its stars. Inevitably the processes governing the early stages of Galaxy evolution are imprinted upon them. According to the currently favoured hierarchical bottom-up scenario of galaxy formation, these components, specially the Galactic halo, are the repository of most of the mass built up from accretion events in those early stages. These events are still going on today, as attested by the long stellar streams associated to the Sagittarius dwarf galaxy and several other observed tidal substructure, whose geometry, extent, and kinematics are important constraints to reconstruct the MW gravitational potential and infer its total (visible + dark) mass. In addition, the remaining system of MW satellites is expected to be a fossil record of the much larger population of Galactic building blocks that once existed and got accreted. For all these reasons, it is crucial to unravel as much of this remaining population as possible, as well as the current stellar streams that orbit within the halo. The best bet to achieve this task is to carry out wide, deep, and multi-band photometric surveys that provide homogeneous stellar samples. In this contribution, we summarize the results of several years of work towards detecting and characterizing distant MW stellar systems, star clusters and dwarf spheroidals alike, with an emphasis on the analysis of data from the Dark Energy Survey (DES). We argue that most of the volume in distance, size and luminosity space, both in the Galaxy and in the Clouds, is still unprobed. We then discuss the perspectives of exploring this outer MW volume using the current surveys, as well as other current and future surveys, such as the Large Synoptic Survey Telescope (LSST).

scholarly journals THE BINARY FREQUENCY OF r -PROCESS-ELEMENT-ENHANCED METAL-POOR STARS AND ITS IMPLICATIONS: CHEMICAL TAGGING IN THE PRIMITIVE HALO OF THE MILKY WAY

2011 ◽  
Vol 743 (1) ◽  
pp. L1 ◽  
Author(s):  
Terese Hansen ◽  
Johannes Andersen ◽  
Birgitta Nordström ◽  
Lars A. Buchhave ◽  
Timothy C. Beers
Keyword(s):  
Milky Way ◽  
Chemical Tagging ◽  
R Process ◽  
Process Element

scholarly journals Traces of the formation history of the Milky Way

2013 ◽  
Vol 9 (S298) ◽  
pp. 430-430
Author(s):  
B. Nordström ◽  
E. Stonkutė ◽  
R. Ženovienė ◽  
G. Tautvaišienė
Keyword(s):  
Milky Way ◽  
Orbital Parameters ◽  
Element Abundances ◽  
Elemental Abundances ◽  
Formation History ◽  
First Results ◽  
History Of ◽  
R Process ◽  
Process Element ◽  
Kinematic Properties

AbstractChemical and kinematical information is needed in order to understand and trace the formation history of our Galaxy. In the homogeneous large sample of F and G stars in the survey by Nordström et al. (2004), groups of stars with orbital parameters different from field stars were found by Helmi et al. (2006). Simulations of disrupted satellites showed that the groups had similar properties as infalling dwarf satellites would have after several Gyr. From high resolution spectra, we analyse elemental abundances of stars in 3 such groups with conserved kinematic properties. Here we present first results of s- and r- process element abundances in two such groups and compare with average field stars.

scholarly journals Kinematics of highly r-process-enhanced halo stars: Evidence for origins in now-destroyed ultra-faint dwarf galaxies

2019 ◽  
Vol 14 (S353) ◽  
pp. 71-74
Author(s):  
Kaley Brauer ◽  
Alexander P. Ji ◽  
Kohei Hattori ◽  
Sergio Escobar ◽  
Anna Frebel
Keyword(s):  
Milky Way ◽  
Dwarf Galaxies ◽  
Building Blocks ◽  
Specific Chemical ◽  
Halo Stars ◽  
Novel Approach ◽  
Chemical Signatures ◽  
Formation History ◽  
Stellar Halo ◽  
R Process

AbstractThe Milky Way’s stellar halo preserves a fossil record of smaller dwarf galaxies that merged with the Milky Way throughout its formation history. Currently, though, we lack reliable ways to identify which halo stars originated in which dwarf galaxies or even which stars were definitively accreted. Selecting stars with specific chemical signatures may provide a way forward. We investigate this theoretically and observationally for stars with r-process nucleosynthesis signatures. Theoretically, we combine high-resolution cosmological simulations with an empirically-motivated treatment of r-process enhancement. We find that around half of highly r-process-enhanced metal-poor halo stars may have originated in early ultra-faint dwarf galaxies that merged into the Milky Way during its formation. Observationally, we use Gaia DR2 to compare the kinematics of highly r-process-enhanced halo stars with those of normal halo stars. R-process-enhanced stars have higher galactocentric velocities than normal halo stars, suggesting an accretion origin. If r-process-enhanced stars largely originated in accreted ultra-faint dwarf galaxies, halo stars we observe today could play a key role in understanding the smallest building blocks of the Milky Way via this novel approach of chemical tagging

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