R-process-rich Stellar Streams in the Milky Way*
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Gull_2021_ApJ_912_52.pdf
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Published version
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Author(s)
Gull, Maude
Frebel, Anna
Hinojosa, Karina
Roederer, Ian U
Ji, Alexander P
Brauer, Kaley
Date Issued
2021
Journal
Astrophysical Journal
Publisher
American Astronomical Society
Citation
Gull, Maude, Frebel, Anna, Hinojosa, Karina, Roederer, Ian U, Ji, Alexander P et al. 2021. "R-process-rich Stellar Streams in the Milky Way*." Astrophysical Journal, 912 (1).
Version
Final published version
Abstract
Abstract
We present high-resolution Magellan/MIKE spectra of 22 bright (9 < V < 13.5) metal-poor stars (−3.18 < [Fe/H] < −1.37) in three different stellar streams, the Helmi debris stream, the Helmi trail stream, and the ω Centauri progenitor stream. We augment our Helmi debris sample with results for 10 stars by Roederer et al. for a total of 32 stars. Detailed chemical abundances of light elements as well as heavy neutron-capture elements have been determined for our 22 stars. All three streams contain carbon-enhanced stars. For 13 stars, neutron-capture element lines were detectable, and they all show signatures in agreement with the scaled solar r-process pattern, albeit with a large spread of −0.5 < [Eu/Fe] < +1.3. Eight of these stars show an additional small s-process contribution superposed onto their r-process pattern. This could be discerned because of the relatively high signal-to-noise ratio of the spectra given that the stars are close by in the halo. Our results suggest that the progenitors of these streams experienced one or more r-process events early on, such as a neutron star merger or another prolific r-process source. This widely enriched these host systems before their accretion by the Milky Way. The small s-process contribution suggests the presence of asymptotic giant branch stars and associated local (inhomogeneous) enrichment as part of the ongoing chemical evolution by low-mass stars. Stars in stellar streams may thus be a promising avenue for studying the detailed history of large dwarf galaxies and their role in halo assembly with easily accessible targets for high-quality spectra of many stars.
We present high-resolution Magellan/MIKE spectra of 22 bright (9 < V < 13.5) metal-poor stars (−3.18 < [Fe/H] < −1.37) in three different stellar streams, the Helmi debris stream, the Helmi trail stream, and the ω Centauri progenitor stream. We augment our Helmi debris sample with results for 10 stars by Roederer et al. for a total of 32 stars. Detailed chemical abundances of light elements as well as heavy neutron-capture elements have been determined for our 22 stars. All three streams contain carbon-enhanced stars. For 13 stars, neutron-capture element lines were detectable, and they all show signatures in agreement with the scaled solar r-process pattern, albeit with a large spread of −0.5 < [Eu/Fe] < +1.3. Eight of these stars show an additional small s-process contribution superposed onto their r-process pattern. This could be discerned because of the relatively high signal-to-noise ratio of the spectra given that the stars are close by in the halo. Our results suggest that the progenitors of these streams experienced one or more r-process events early on, such as a neutron star merger or another prolific r-process source. This widely enriched these host systems before their accretion by the Milky Way. The small s-process contribution suggests the presence of asymptotic giant branch stars and associated local (inhomogeneous) enrichment as part of the ongoing chemical evolution by low-mass stars. Stars in stellar streams may thus be a promising avenue for studying the detailed history of large dwarf galaxies and their role in halo assembly with easily accessible targets for high-quality spectra of many stars.
MIT Department
Massachusetts Institute of Technology. Department of Physics
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.3847/1538-4357/ABEA1A
