Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass Stellar Nucleosynthesis
Journal
Date Issued
2020
Author(s)
Hansen, T. T.
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Marshall, J. L.
•
Simon, J. D.
•
Li, T. S.
•
Bernstein, R. A.
•
Pace, A. B.
•
Ferguson, P.
•
Nagasawa, D. Q.
•
Kuehn, K.
•
•
Geha, M.
•
James, D.
•
Walker, A.
•
Diehl, H. T.
•
Aguena, M.
•
Allam, S.
•
Avila, S.
•
Bertin, E.
•
Brooks, D.
•
Buckley-Geer, E.
•
Burke, D. L.
•
Rosell, A. Carnero
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Kind, M. Carrasco
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Carretero, J.
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Costanzi, M.
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Da Costa, L. N.
•
Desai, S.
•
De Vicente, J.
•
Doel, P.
•
Eckert, K.
•
Eifler, T. F.
•
Everett, S.
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Ferrero, I.
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Frieman, J.
•
García-Bellido, J.
•
Gaztanaga, E.
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Gerdes, D. W.
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Gruen, D.
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Gruendl, R. A.
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Gschwend, J.
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Gutierrez, G.
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Hinton, S. R.
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Hollowood, D. L.
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Honscheid, K.
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Kuropatkin, N.
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Maia, M. A. G.
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March, M.
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Miquel, R.
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Palmese, A.
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Paz-Chinchón, F.
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Plazas, A. A.
•
Sanchez, E.
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Santiago, B.
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Scarpine, V.
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Serrano, S.
•
Smith, M.
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Soares-Santos, M.
•
Suchyta, E.
•
Swanson, M. E. C.
•
Tarle, G.
•
Varga, T. N.
•
Wilkinson, R.
•
DES Collaboration
Abstract
We present a detailed abundance analysis of the three brightest member stars at the top of the giant branch of the ultrafaint dwarf (UFD) galaxy Grus II. All stars exhibit a higher than expected [Mg/Ca] ratio compared to metal-poor stars in other UFD galaxies and in the Milky Way (MW) halo. Nucleosynthesis in high-mass ( $\geqslant $ 20 M☉) core-collapse supernovae has been shown to create this signature. The abundances of this small sample (three) stars suggests the chemical enrichment of Grus II could have occurred through substantial high-mass stellar evolution, and is consistent with the framework of a top-heavy initial mass function. However, with only three stars it cannot be ruled out that the abundance pattern is the result of a stochastic chemical enrichment at early times in the galaxy. The most metal-rich of the three stars also possesses a small enhancement in rapid neutron-capture (r-process) elements. The abundance pattern of the r-process elements in this star matches the scaled r-process pattern of the solar system and r-process enhanced stars in other dwarf galaxies and in the MW halo, hinting at a common origin for these elements across a range of environments. All current proposed astrophysical sites of r-process element production are associated with high-mass stars, thus the possible top-heavy initial mass function of Grus II would increase the likelihood of any of these events occurring. The time delay between the α and r-process element enrichment of the galaxy favors a neutron star merger as the origin of the r-process elements in Grus II. * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile....
Volume
897
Issue
2
Start page
183
Issn Identifier
0004-637X
Ads BibCode
2020ApJ...897..183H
Rights
open.access
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