Signature of a massive rotating metal-poor star imprinted in the phoenix stellar stream
Date
2021
Authors
Casey, Andrew
Ji, Alexander P
Hansen, Terese
Li, Ting S
Koposov, Sergey
Da Costa, Gary
Bland-Hawthorn, Joss
Cullinane, Lara
Erkal, Denis
Lewis, Geraint
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IOP Publishing
Abstract
The Phoenix stellar stream has a low intrinsic dispersion in velocity and metallicity that implies the progenitor was probably a low-mass globular cluster. In this work we use Magellan/Magellan Inamori Kyocera Echelle (MIKE) high-dispersion spectroscopy of eight Phoenix stream red giants to confirm this scenario. In particular, we find negligible intrinsic scatter in metallicity (s([ ]) = - Fe II H 0.04+0.03 0.11) and a large peak-to-peak range in [Na/Fe] and [Al/Fe] abundance ratios, consistent with the light element abundance patterns seen in the most metal-poor globular clusters. However, unlike any other globular cluster, we also find an intrinsic spread in [Sr II/Fe] spanning ∼1 dex, while [Ba II/Fe] shows nearly no intrinsic spread (s([ ]) = - Ba II H 0.03+0.02 0.10). This abundance signature is best interpreted as slow-neutron-capture element production from a massive fast-rotating metal-poor star (15-20Me, vini/vcrit = 0.4, [Fe/H] = -3.8). The low inferred cluster mass suggests the system would have been unable to retain supernovae ejecta, implying that any massive fast-rotating metal-poor star that enriched the interstellar medium must have formed and evolved before the globular cluster formed. Neutron-capture element production from asymptotic giant branch stars or magneto-rotational instabilities in core-collapse supernovae provide poor fits to the observations. We also report one Phoenix stream star to be a lithium-rich giant (A(Li) = 3.1 ± 0.1). At [Fe/H ] = -2.93; it is among the most metal-poor lithium-rich giants known.
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Stellar streams
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The Astrophysical Journal
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Journal article
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